DC were at their dads. Due home at 5pm today.
I was in town doing some shopping and heard a kid crying from the other side of the shop which sounded like DD. Went to look and found all three DC with a woman I've never seen before dragging DD by her hand out of the shop 
Obviously I stopped her and said WTF are you doing and who the hell are you.
Turns out she is the best mate of ex's girlfriend. Ex had to work so left kids with his partner. Partner decided to take them to town with her mate. Partner then went to get her hair blow dried at one of those pop up blow dry places and left DC with her mate. Youngest DC (5) was upset and refused to leave the shop. Big department store so she had managed to get her three floors down during the tantrum.
DD asked to come home with me and then the other two said they wanted to as well. The woman starts saying I couldn't take them as she didn't know who I was. Oldest is 11 and clearly saying that's my mum!
Anyway I took them as they are due home soon anyway.
EX has just phoned and gone ballistic that I had no right to take them and partner is frantic about it.
AIBU to take them home with me?