First, did I read that this is your first post? Welcome

So far as snacks go, think back to when you were a kid. In my family a snack was just meant to hold us over till dinner....it wasn't a food free for all. When I worked in daycare centres, snacks were small and there was typically one serving for each child. It was intended to keep the blood sugar up enough to get through the day....just a little something. One serving is ample for the snacks you've described. I've no doubt they want seconds as they're more 'treat like', even though they're healthy. What I do, with kids 18 mos and up, when they don't eat their lunch is to give it back at snack. If it's a messed up pile of mush, then no, it goes in the compost, but intact food is returned. If they're hungry, they'll eat it, THEN get the snack. So far, it's been successful.