Although we're the other way around,I discussed the move with my two daughters(then aged 9 & 11)of the move to England from the very start.For me personally,it was important that we discussed the move as a family.I would not have moved had my daughters objected.At the end of the day we all had to be happy,not just me.Of course my kids are older than yours.Not sure at 2 and 5 if your children will be able to take it all in.I guess if you don't tell them now,your other family members.friends might spill the beans accidently and you'll then have some explaining to do.If no one else knows,I would probably wait and tell them when its abit closer tbh.Even a month to a child seems like a long time.