What time do you need to leave to do the school run? Eat 20-30 mins before that if possible. If it were me though, I'd ask that the school agers bring their own snack (or I'd supply it...easy and quick things like granola bars, toast, English muffin etc paired with some fruit) and they can eat that before leaving and than I'd feed the little ones after getting back home.

When do they get back to your house? I'd likely do nap 1230-230, feed the littles snack, pick up school kids and they could eat snack when back at your place. I know some might not like that because it's 2 diff snack times but honestly, school agers are more than capable of eating snack with you just checking in on them and they can be responsible for cleaning up.

I don't have school aged kids so my schedule won't be any help but snack is anywhere between 9/930, lunch at noon, nap at 1230/1-3 and snack is done by 330