[bluGill]

Kids are mentally not ready to read before some age, and once they are able to learn it takes a lot of training. you cannot assume a 7 year old is a good reader - even if they are the best for their age they are still really bad at it.

if you want quick usage a good graphic is faster than text for simple concept even in the best readers. if you have complex concepts eventually text is better but for the majority of ui text is worse than good graphics for the great reader, and many adults are not great readers.

you also shouldn't assume any language. a little effort with non text based and your app doesn't need expensive translation.

of course a learn to read app needs to provide text. However for most apps text is a sign that you didn't spend enough time in ux design.