Toddler being bullied

Cassie

Hey guys, looking for advice, my 2 year old is a very timid gentle boy and his friend also 2 years old always is punching, pushing, kicking, hitting him etc. I'm just not sure what I should do about it. Obviously kids will be kids, but I just don't feel like I need to subject my son to that and his friends Mom is my best friend so I'm not sure what to do. Opinions?