lifting heavy grandchild

Its the lifting and twisting at the same time that puts your back at risk. Teaching them to climb in and out sounds like excellent advice. Its certainly easier the younger you looking after littlelies.. I even found just holding my 8mth old grandson on my hip made my back ache a little I know I wouldn't be able to do it on a daily basis.

I hope you manage to find the answer , then you can tell the rest of us.

Getting them in is the hard part. Until I realised I could put my knee under the child's bottom and ease them across and in. Was a doddle after that.

Child car seats are the work of the devil, from the GP's point of view.
Suggest back-strengthening exercises, and teaching GCs to climb into and out of their car seats themselves.
That is what DD and DDil have done.