I usually make my sims make a sack lunch for their kids. They never really bothered eating it at school, I am going to guess that it was because their bars were still green. As much as I like the idea of having to prepare sack lunches for your sims, it is a real disappointment that some will not bother to eat it while they are in their rabbit hole.
There are some perks for sack lunches at least for me anyway. When I make the kids go out to a public park I would usually have to send an adult or a teenager with them. If I did not have an adult or a teen, after all of that playing the kids did, they become eventually hungry and they are basically out of luck and would have to leave the park in order to get some food.
With sack lunches I do not really have to bring teenager with them or an adult. They can go play on their own without having to depend on an adult to fix them hotdogs and hamburgers.
