Impressive that Thomas managed to push both and still keep up with you!
I realized when I wrote this it sounded a bit odd, do I need a comma? I guess I should have put Ivar, and Thomas pushing the stroller.
I think it's perfect the way it is. Only people who don't know Ivar would assume that he wasn't the one sitting in the stroller.
I, myself, would make no assumptions with Thomas and Louise.