K.H.
Hi L.! We JUST went through this (literally last week) with our 2.5 year old. I think going over there a lot prior to moving in will help. The few things we did that seemed to help:
1) Let him help you unpack and put things where they belong (when he can - i.e. towels, bedding, etc)
2) We had her grandma take our daughter shopping (or to the park or whatever) while we got her room set up. That way when she came back her "old" room was magically all assembled just the way she would remember it and had all her treasures in it!
3) Designate a "play area" really early and put all his favorite toys there. He will feel like he has his own "area" in the home.
From there its just been reinforcement. She is fine during the day but at night, for the first few days, she would cry and want to go "back home". We just lovingly but consistently told her that this was our home now and that we live here. Its been just over a week and things are much improved.
As for the 9m/o I would say just try and keep her close to you as much as possible and again keep her room or area as familiar as possible as soon as possible.
Best of luck and I hope you LOVE your new home!