How do you do it?

I don't have a bad back so I can easily do bath tub backs and do diaper changes on the floor.

DH and MIL have bad backs so they can't do that. Our infant tub fits in the kitchen sink so they can stand. For diaper changes, they use the changing table. But now that they are getting squirmy, I have resorted to changing them on the floor because I don't have to worry about them rolling off of it.

So how do you do it?

I have heard from other friends with bad backs that having kids made their backs worse.