My 3 year old keeps hurting other children

[AlwaysNeverOnTime]

I never had this with my older child and I really don't know what to do. My DS is 3. His speech isn't great and I struggle to understand him about 50% of the time. He gets extremely angry and frustrated when I don't understand him. He's only recently started to put more than 2 words together which is think is part of the problem. He's been to speech and language, but they told me that they would only expect a child of his age to put 2 words together and weren't concerned. I work with kids so I disagree. DS comes to work with me and he's constantly attacking other children. It's never unprovoked (not that it makes it any better) but he will go crazy at the other child grabbing at them, scratching, hitting and occasionally biting if I don't get to him in time. I'm watching him constantly because I'm always on edge. I'm so embarrassed by his behaviour and have cried many times because I feel so bad for the other kids. One boy who he is friends with, ends up getting hurt quite a lot which is awful. I do time out and I do try talk to him but it's so hard to know if he actually understands what's I'm saying. Any suggestions? I'm considering leaving my job because of this because I don't feel like he should be around other children.