When my twins were little, I was at a school conference and was informed there was a problem: one took toys from the other without asking.
I asked this teacher "Is the one who had the toy taken upset when this happens?" She replied, "No."
"Is it the same one who does it every time?"
"No, they both do it."
"Do they do it to other kids?"
"No, only to each other."
"Do they share with others?"
"Well, what's the problem? It obviously works for them, isn't harming others and they obviously have learned how to interact appropriately with others."
She had no answer for me.
These same girls are now in their early twenties and are generous, cooperative and still take one another's clothes.
They have two older sisters and all spent many hours playing with commingled Barbies and plastic ponies and as a result learned how to negotiate for toys and control of play. I kept my interventions to a minimum and I think it worked well. Complainers were told they didn't have to stay in the game, but they rarely left the play.
Bottom line, kids need to play without adults micromanaging. They learn valuable skills that adults can enhance if they teach how to manage the current conflicts. Adults should only intervene if one child is in danger from the other child being out of control and redirecting is the best tool. Children need to learn how to respond to their emotions and desires more than they need to keep some arbitrary adult standard of equity - most are not living in a "Lord of the Flies" situation.