where can in learn simple hair cutting for children in the community centre in town area?

Answer 1

Take one bowl.
Place over child's head.
Cut around said bowl.
Repeat for next child.
And so on.

Answer 2

I bet if you go to a couple local salons someone will teach you. Offer to give coupons to their salon or even just business cards when you do your haircutting. People love free advertisement. It is usually fairly easy to get someone to agree to teach you something for a good cause. After all it wouldn't take too much of their time. :)