Theoretically yes, since I think it might be less likely the 3 year old would get the help/support they need to recover from the trauma especially in an abuse situation they could be stuck in a tramatizing environment with no way to leave it... Also just having a lack of support/help after a traumatic event can increase chances of developing PTSD from it so even if the child has a good family if they aren't able to provide the right support/help which based on 3 year olds maybe having less ability to verbalize their symptoms and what not...or if the family doesn't know about the traumatic event.

So I think it sort of depends on the situation, but not so sure it's being a young age specifically that would make PTSD more difficult to fight...or if its more not really having any support or help to get through it.