At the age of seven, namaz becomes compulsory on the kid and at age of 10 parents can beat their kid if he does not care for namaz. Roza is fard at age of puberty. As soon as kids reach their age of puberty, they are entitled to observe fast.
Why is it made compulsory at young age? The reason is, since at the early age, children learn fast and they understand easily, at the later age, people are more ego struck and to exercise religion becomes difficult for them. How to tell you kid and prepare him for Ramadan? There are few pointsc to be taken into account.
1: before asking your kid to fast at his proper age, make him understand the reason why we fast. Tell him how good it is to fast.
2: kids are curious to know each and every thing, they ask questions, so be patient to them, and while telling them about Ramadan, learn authentic and good knowledge.
3: tell them at their younger age to observe little fasts with you, in this way they will be abel to learn how to fast and how mom and dad fast.
4: do not discourage your kids if they ask to fast with you. Let them observe and if in the middle of the day, they cannot make it through, do not enforce them to wait for the aftar.
5: make sure that kids wake up at sahar and they are present at aftar. Given them equal importance and deal with them gently so that they also feel urge to fast.
6: tell them to be good kids while having fast. In this way kids will learn to be good and to avoid bad things in Ramadan.
Prepare your kids for Ramadan so that when roza becomes obligatory, they do ntohave any trouble observing fast.