A: Dear Rebeccamalinsk:
If your son has been able to squeeze his friends for as long as a year (for nearly half his life!), then this is a pattern which might be hard to change overnight. It is often the case that toddlers who are energetic, aggressive, and physically large or powerful tend to bully other children who are not able to put up an effective resistance.
The ideal solution is to put your son with a different group of preschool children who are several months older, and therefore bigger and stronger than he is. He will then discover that he is unsuccessful at squeezing these children, and give up trying. If the preschool is able to make this sort of change, you might be amazed at how "new friends" are a simple solution to your son's problem.
Otherwise, you will have to have an adult supervise very closely, so that the adult can stop the squeeze before it gets started, saying calmly but firmly, "No no--we don't squeeze." The minute your son succeeds in squeezing the other child, his attention is on to something else. Trying to scold or impose consequences afterwards is unlikely to be very useful, and may only make your son feel more aggressive inside.
Elizabeth Berger MD
Child Psychiatrist and author of "Raising Kids with Character"