I also have a ten yr old, boy on Concerta, he has no appetite either. We tried a few other meds, but Concerta seems to work the best - other than the appetite... My son is pretty thin, but he doesn't lose weight anymore due to feeding him "Ensure"... He eats a really good breakfast - that is about it.... We offer lunch,,,healthy snacks and of course dinner....He most of the time just picks eats very little, so after eating we make him drink an Ensure.. He drinks 3/4 daily....---They don't taste the best---(actually my son likes them) but my doctor said you can mix them with stuff, ice cream,,,ice,,,whipped cream,,, anything to get him to at least get the nutrition they need.
Hope this helps - good luck!!