Since starting in a nursery a few weeks ago 3.5yo pretty much wants 4 meals a day. I suspect it is dinner being earlier than she's used to at home, and possibly she's just not eating too much. So she's having breakfast at 8, lunch at 12, dinner at 4 - and then at 6-6.30 she is ready to eat a whole meal again, no bananas fobbing her off. I don't really blame her as at home she probably won't eat dinner until 5-6ish, so being hungry 2-2.5 hours after her last meal isn't much of a surprise.
So far we've been giving porridge or weetabix, which she'll eat a massive bowl of and sometimes still want fruit or cucumber or something similar afterwards (which means she genuinely is hungry, not trying her luck for a biscuit). This doesn't seem very exciting though, but at least it's quick to make.
Any other suggestions?