QueenJane already mentioned it, but yes do not think the younger the child the less imapcted. My kid with the biggest issues came to us at 2 1/2, and the next one at barely 2. We deal with HUGE behaviors here. Not trying to scare you, but I was totally uneducated when we started. I also do not suggest getting a child slightly older or really close in age as your bio child. I would have not disrupted birth order like we did if I had to do it all over again.