Using a thermos is one of the easiest ways to keep food safe. To prevent the growth of harmful bacteria in hot foods preheat the thermos with very hot water before adding the hot food. Pre-cool the thermos with ice water before filling with cold food. With a good thermos you can send frozen fruit sorbet and be confident it will still be frozen when your child is ready to eat it for lunch.
Freeze bottles of water, juice boxes or other containers overnight