Feel about children pain
First thing to do when handing children that being teased understands their feeling. In fact, it is hurt enough to being teased. Show your sympathy so that they can talk freely about it and how to cope with it.
Teach how to ask for help
Most children may do not strange about preschooler teasing habit. Teach child to talk to you as provider to get help since the age of them and the bullies is too young to understand how to cope with it properly.
Never make any joke on teased children
You better never ever try to make any joke that makes children feel ashamed. At least you will need to show your empathy and affection on them. Any sentence that makes them shame will only bring more burden. Name calling is also big no no especially in front of their peer. Doing it will make children learn the limit on words that will not hurt or shame other.
You may think that they are too young to understand. In fact, preschooler carefully notice about everything and vocal about it. Children are also doing teasing only as an act to find out the reaction of their words.
Teach child to show empathy
Be sure that you teach earlier so that children can understand about the responsibility of what they have said to other. Let them know the reason behind putting yourself into another person shoes. Remind them that it will make someone feel bad when they are talking too loud or too short. You also need to remind them from making any negative comment on another person appearance.