Not sure whether IABU or not.
Just found out that ex spent a few hours at a drinks party leaving our DCs (13, 10, 6) with another friend. I assumed she looked after them but she went to the party too, leaving her 2 DCs. Then turned out another child stayed to play. So that meant 6 DCs aged 13 to 6. Someone checked on them every half hour or so 'and they had our mobile numbers.' The party was for grown-ups only.