Toddler bullying his classmates

My 2 almost 3 year old son, the past 2 weeks, has started to push and hit several of his classmates at school. He never used to be violent towards anyone before. Now everyday I go to pick him up his teacher tells me how bad he behaved. I am also 7 months pregnant and when I hear this stuff it makes me really sad. He isn’t as verbal as the majority of his classmates as he has a speech delay related to undetected glue ear until almost the age of 2. He is generally a happy kid and loves being around other children. Like I mentioned previously, he just all of a sudden started doing this recently. I don’t know what to do to get him to stop. Any suggestions?