My mother in law used to do this. Our house is small and one time she came over all the toys were out, included a huge hot wheels garage taller than my kid and a motorized bulldozer that could pull 50 lbs. I think she realized that there literally is no space and since then bought fewer and smaller toys. But she is also a person who likes to keep her house tidy, so if the grandparent is a hoarder, this might not change.