Question: His grandparents think he shouldn't read a book suitable for a three year old or play with cuddly soft toys (even though those are only associated with his love of Pokémon). His grandparent also don't like anything even slightly related to Pokémon. My son doesn't play enough as it is—too obsessed with computer games, videos, making stuff or writing (not that he writes sentences).

For me I am happy if he reads anything or plays with any toys, especially if he has fun. Is there any research to say you should get rid of younger child toys?

Answer: 
Cuddly soft toys are most certainly age appropriate, and in fact most of the Pokémon plush toys are at least age 4+ if not higher. They're great for creative play, and are especially useful if there's nobody else to play with (as the plush can take the role of the other person - think Calvin and Hobbes). This kind of play is extremely valuable at this age (and continues to be valuable as they get older) as it lets them explore different things from their life and grow emotionally in a safe setting. It also helps develop [empathy and social skills](https://blog.frontiersin.org/2020/10/01/human-neuroscience-child-play-dolls-cognitive-social-benefits-children/).

Books that are aimed at a younger child will not challenge him, but it's reasonable to separate "reading for fun" from "reading challenging books". My children, who are now pre-teens, still read picture books from time to time; they're both extremely high achieving readers (3+ grade levels ahead), so it hasn't stunted them meaningfully. Instead, it's a fun thing for them to do. They *also* read more challenging books, but that's separate from reading fun things that are nostalgic or just fun. They also may [pick up more complicated concepts](https://childrenslibrarylady.com/using-picture-books-with-older-children/) than they did as younger children - think about how rereading a book as an adult works; this won't apply to every picture book, but some are quite complex and have value for both younger and older children.
I mean I'm 24 and I still play with LEGOs, model trains, action figures, basketballs, water guns, water balloons and such, I could go on. Ridiculous? Maybe, but it's also what helps me kick back after long hours of working, studying what have you. Oh and I've still held on to a number of my old plushes as well (ok granted they're more room decor now) because they still have deep sentimental meanings. Your son is 7, not 37, he should absolutely partake in anything that's constructive for him and tell his grandparents to take a hike if they have such a problem with it. At least he isn't out skipping school or bullying other kids.