First, remember that a small child does not need to fast, and the first year you might have the child fast only on the weekends. (However, it might be easier for the child to fast when outside the house and busy so that the temptation to snack isn’t always there.)
For a young child (7 to 10), I would send some food to school, though perhaps not as much as usual. But this must be done delicately so that you’re not giving the message that you think the child is incapable of fasting.
You should be encouraging. Tell the child that fasting is difficult but that you think he or she can do it and that you are proud of him or her for trying. Tell the child that you will pack some food for school “just in case” but that you want the child to try really hard not to eat it, not to give in at the first pangs of hunger. The child should be encouraged to eat only if he or she feels faint.
Many people who were raised Muslim tell me that they fasted as early as 7 years old with little difficulty. I think that parents who have converted to Islam and thus have never experienced fasting as a child worry more. Have a positive and encouraging attitude at all times.
If there are few or no other Muslim children in your child’s class, you might consider asking the teacher if your child could sit somewhere else during lunch break—perhaps in the library—rather than sitting in the lunch room watching the other students eat. The child should not be left unsupervised and should not be made to feel that this is a punishment. Rather, tell the child that this might make fasting easier by not having to watch others eating. The child should have the option of doing this on a day-to-day basis. In any case, you should inform the teachers if your young child will be fasting on any school days.
An older child (10 and up) should be in serious training for fasting, and I would not send food to school. If the child really has to break the fast early, he or she can do it after school. But I would then remind him or her that there are only a few hours to go and that it would be better to keep fasting. An after school nap is usually a good idea for a child (or an adult) who is fasting.