My child is between sizes (44cm), should I size up or size down?

This is the tricky size area - there is a big difference in the sizes in this range, so while the 42cm will likely fit a 44cm head, it won't last as long as the 47cm, which will be a little big for a little while. But if you choose the bigger size, pull the hat right back behind their head, down on their neck and use the chin strap to keep it in place and they shouldn't be too bothered by it.  A toddler bucket in the bigger size will also seem a little smaller and perhaps fit better straight up due to the seam all the way around the inside which gives it a little less stretch than the legionnaire.

This short video also can talk you through sizing advice: https://youtu.be/tlnf5mlflUY