The short answer
Children handle a move well when they know what is happening, keep some control over their own things, and see their room set up first at the other end.
Three rules cover most of it:
- tell them early and honestly, in language matched to their age;
- let them make real decisions about their own room and belongings;
- keep routines identical through the disruption — same bedtime, same story, same cup.
And one practical rule for the day itself: young children and moving crews should not share a space. Arrange childcare for move day.