Am I wrong in this situation

Lil Queen

I live with my sister in law and my niece has a kitchen oven toy that is kept in the play room for everyone but it is here and its in the closet with hers clothes in it. So my son is 3 and wants to play with it and was and my niece who is 6 is crying and angry because hes playing with it because its hers. So shes about to throw a tantrum so I quickly pull her away from my son and tell her its just a you its ok if hes playing with it and as I'm pulling her away her mom walks in. So am I wrong? It is her toy but like is it not okay he was playing with it first I dont know