My 2nd daughter (18 months at the time) would jump on the bed and land on my stomach. Like she was a wrestler. My nephew (3yrs at the time) who has a sizeable head would ram into my stomach like a bull. My 3rd came out just fine. She's now 3yrs old and tougher than nails. Lol
No, I don't think a two year old is strong enough to hurt baby just by hitting! Baby is very protected and cushioned in there. He/she is fine!