the problem with once a day is:
you give them alot, they cant eat it all at once. by the time they feel hungry again, some has wilted, lost its juicyness, etc... just not as nice and tasty anymore. also, if they are outside, ants etc can get to it.
In summer its especially dangerous, as flies like to lay eggs in leftover food.
so if you make it two portions, one in the morning, one in the evening, its alot better
maybe you could ask your parents to give them the first portion mid-morning, if you dont have the time to give it to them before school?