@Ayman,
Hi
First off you might want to use a toy or puppet of some kind that will get them focussed more on you or the puppet.
Talk slowly to the children not too fast.
Use simple words that they will understand.
Don't have them sat down for too long listening to just you.
Get them to join in answering questions and asking questions etc etc.
Smile at them and appear friendly so that they relax with you.
Hope this helps!