Hi WM,
I think whatever way you do things, you had better get your husband a comfy 'ride on' rucksack
I took my 3 1/2 yo lad up Plaice Fell and carried him up the last bit and all the way down on my shoulders and rucksack !!
We didn't half laugh about it,
Luckily enough now he is nearly 15 and has two independant legs, sorry not much help for now, just thought I'd share what I think is a quite common experience.
Gook luck,
Graham