My son is mean lol

My sons 3, 4 in Feb.

he is mean to the little kids man, he pushes kids. I don’t know what to do! He even pushes his 15 month old brother. He started daycare on Wednesday last week, he already had an accident report. He pushed a kid then that kid hit my son back & made him bleed.

He’s always pushing kids down. What do I do? His teachers tell him “it’s not nice to push our friends” but yeah, I don’t think that’s enough of a “punishment”

When he pushes his brother I tell him “don’t push your brother!” (More so- in a loud tone cuz he makes his bother cry). Lol