Little girls who are toddlera so not need to wear tops. Their physically immature state has no yet started to make her breasts look any different than boys of the same age. Typically little girls show no female-change in their breasts until about 8 years old at the earliest. That is also when child play (3rd grade) starts to separate between boys and girls. By then little girls begin to wear bathng suits with tops.
Best to start the social training early.
Tempest in a teapot for both sides.
I am thinking that it is because of the pedo predators that are out there.