All sensible riding folk will of course spend at least 3 months leading up to a snowboard holiday squatting (not sitting) when they go for a shit, doing 100kg leg presses in the gym and strengthening core muscles with daily yoga sessions.
If you were not doing this before you had kids, you need to get with the programme because it is WAY more physical teaching kids to ride than just shredding on your own.
You will lift your child up out of the snow 100-200 times a day. You will be walking back up hill, a lot. You will be carrying them down the slope when they go into meltdown. You will be dragging them through the flats. You will be pushing them uphill. You will be heaving them onto chair lifts and pulling them up drag lifts.
Basically you need to be a cross between Thor and Mo Farah, so hit that StairMaster, bitch.