A lovely idea someone once shared was to spread out the childrens’ musallas too, from a young age, and whether they joined you or not!
Even if they come and sit down on the mats for a bit while they do something else, it is getting them used to the concept. If they happen to pick up the tasbih and/or do a sajdah, then all the better
And check out these awesome child-friendly prayer mats i just found on google!
P.S. An idea was sent in on facebook to suggest making a miniature Kaaba and placing it in front of the musallas for them to pray towards, to make it all the more magical 🙂