Perfectly Fine. My children were 13-14 months an 3 yesras old when we got our boxer. They all get along fine. She was nuetered at the 8mo range, and nothing has changed. Actually she gets along better with the younger thatn the older. She seems to know that the older is big enought o play , but that the little one isn't yet.
I had actually researched before getting a Boxer, and I'm happy with the choice.