Oh dear, I am an expert on moving house with children as we are in our sixth house since having the children.
The good news for you is that at the age they are, your children should not be too badly affected. I would say that the 4 and 1 yos would not be affected badly at all. The 6 yo might be, it depends on his/her personality/friendships groups at the moment/etc.
At our last move, my children were 8, 7, nearly 5 and 2. The youngest was unaffected and the oldest quickly adapted and actually has never looked back as, at his old school he was not really accepted by the other children and had only one (sort of) friend, whereas where we are now, he found instant acceptance and has loads of friends. So for him, the affect was positive.
The 5 yo was a bit sad for a while but is very popular in her class and cannot really be said to have been affected longterm. She now (2 years on) hardly remembers anything about her old home and friends.
The worst affected in my family was my 7 year old who was very popular at his last school but has found making new friends very hard. He would cry on and off for months after the move and was always wanting to go back "home". He also had medical problems which I am sure were exacerbated by the move. He is better now, but I am sure he would still say all in all, he would rather our last move had not taken place.