I have never heard that at 12 kids no longer learn.... I think that is likely a myth. Though, usually, around that age puberty starts to hit hard and things can get 'interesting' and they are ogften less compliant and they develop their own will and sense of self and may do some rebelling..... For several years.... My sister didn't start to get over it till i think.... 2 weeks before she turned 17.
So if that natural development gets in the way.... It gets in the way... But a massive amount of our social education and self awareness and slightly more advanced academics happens in years after we hit 12. What would the point be to all that if kids were somehow less able to learn after age 12?
The best thing you can do at that point, is to help them develop their identity and accept some choices will be good some won't. But either way they will keep learning. And they have the values somewhere in there instilled by your son and his wife with your help. Support their self discovery and their discovery of everything else too. It might even be good for their learning in that, they will be thinking of all sorts of things in relation to their identity and beginning to question the world, and where they stand on just about everything. But that means they will have to learn about these things. Reading is a great way to do that.
As for summer.... I realize everyone thinks they are way behind, and they probably are.... But sometimes the best way to help, is to treat them normally like normal children. Children work very hard in school weather they are 'normal' or labled. Sadly everyone wants to 'improve' those of us labled so much that we never get a break. I quit college in the middle of my first semester. For just that reason.... I was miserable and i wanted a break and my senior year my parents like had me in special programs forcing me to write college essays and i think i spent 4 blocks in one day in highschool in resource related to writing essays... Along with another 2 blocks over the course of the week.... waaaaaaaaaaay too much.... Especially, because they knew i really wanted to just take a year off. Education systems were very hard for me and going through one for 12 years and all the summer schooling because i am not normal and the constant breathing down my neck..... When i was a C average student.... was.... over kill. And even if i wasn't a C average student, i tried... and that means i worked hard. And that means i am as normal as other kids who work hard and they get a vacation. Getting a few games that are phonics based for rainy days, and for the odd evening and for some bonding is a great idea! It would also be prudent to try to avoid overworking them and making them feel abnormal, it will make them feel down about themselves and then you are looking at a worse pubesant period.... Plus, they may start to resent you, for being the one to continue to "work' them while everyone else gets a break. They are learning disabled and not stupid. which you well know. They have eyes and ears and know othher kids are off having fun.
Now, your house your rules, which means, you can find special things for those who choose to read. For example, for every half hour they read or work on reading they get an hour of time they can watch tv, and keep track.... Encourage them to read, make them want to read.
What subjects do they like? Find out, find books on those things, kids want to be like adults, the more you all read, especially if you read cool books about subjects they enjoy.... The more enticed they might get... This is manipulative most definately, but it leaves room for them to choose during what is their vacation, how they wish to spend their time, which is only fair as it is their vacation. Plus the more a child is hmmm made to do something the more they resent it, especially if it is hard for them. And Don't just work on reading! Find things they do well, and try to encourage those things as well, and make sure there is also insentive for them to do those things, so he doesn't see the trick you are pulling, to get them to read. Never should they be punished for saying they don't want to read. Never should they be rewarded for what they didn't do. But it is important that they see the value placed on what they are good at. Though, i would rather than for example hour of tv for half hour of reading, maybe instead with math if they are good at that, a fair trade half hour for half hour. That way reading becomes the quickest method and wasts the least amount of their summer working. leaving them more time for fun. Muahahahaha The other thing that is important is if you see them reading, to earn tv or something else, to equate reading even more with positive things, maybe go get them a couple cookies and a small glass of milk and tell them how proud you are to see them reading. But it is crucially important, they never associate bad things with reading or sadly its likely over.
The other thing peoople forget about reading is just what a crucial part of our lives it really is. And how many mediums and purposes it serves. Maybe a pen pal? You can help them write their letters.... And read those they receive, etc.... Or go to some museums with exhibits they like and if they say cool when they see it, point to the small blurb, and tell them if they read that one you will read the nexxt one so that they can really see how cool it is. Encourage other formats for the use of reading, right now they equate it with school which no kid really enjoys, and with probably bad experience and even possibly with nastiness from other kids who can do it better. Using street signs, and other mediums of text.... Is a total snow job and can be very useful. Think smart, think evil, Ask yourself, how would the Bush administration do it? (As they are masters of manipulation, just look at all the synthetic terror and we are all begging to sign away our constitutional rights and all our freedoms to be 'safe.') And half the population maybe more, doesn't even realize... If the same can be said for your grand sons about reading, (however leave out the water boarding and the abu graihbs and stuff....) They will likely do it without realizing what they are doing. It will get easier and easier.... And soon hopefully it will be second nature. Then, they won't need to be encouraged. Because it won't be hard, and they will have fun while they do it.
Another way to do this, is to read plays... They are too young for Shakespeare, or to encourage them to be dramatic, by helping them script play time.... And then reproduce it or get them into a local drama program or something drama based, where they get to stand it up and act it out, if they are the sort that enjoys drama. Tell them, it is like a TV show without cameras. Another thought would be to get them a video camera and help them to record it like a TV show... Like the stars...
Your house your rules, tell them if they want to go somewhere they have to submit their request in writing. Make sure they know you will take them just about anywhere that they will write that they want to go, or that you will help them or do with them any activity that they write that they want to do. Make it part of life living in your house.... But don't force it into their day as like sit down school studying.... Bad idea... *i* think anyway. You could also switch off reading pages of a book till it is done, and then rent them the movie. Also if they want to go somewhere and you are not there or whatever, encourage them to write a note, like to say they are going to visit the neighbor or to the candy store a block away or something... Get them into new activities and new games, but don't *tell* them the rules.... Have them read them. And offer some small incentive on top of the game or activity itself to be sure it is then worth while.... Rent a a foreign movie and realize it may take 24 hours of pause unpause to get through it. Fun with food, you could get simple cook books and recipes and help them to cook stuff they will like to eat, Also, you can write, *with* their food on their plates something nice like 1 word that is very, complimentary. Make it part of your home, don't make it an academic practice. Its their time off. That is my advice.... but then, i am not an educator, just a woman who had a hard time learning to read and write dyslexic and ADHD, that has had some fabulous teachers and experiences with people who really helped me, but part of how they did it, was by taking the academic out of the academic. Made it 'life.' made it worth my time as far as fun as a pay off. And left it *my* choice, acknowledging that i am an intelligent person label or no label, able to make such choices. They also, respected how hard i worked all year in school and helped me make the most of my summer at the same time. So the more ick i did, the more fun vacation i had. What kid wouldn't choose that?
Hope this has been of some help, good luck!