I live in a block of flats and share a garden with 4 other families. We all have children under the age of 6 and they play together in the garden, often unsupervised.
Ex-p was over for dinner and said 'I think someone needs to have a word with M (4 year old boy), he's got S's (3 year old girl) knickers off and is tickling her between her legs'. I wasn't particularly worried but went to the balcony to check on them. By this point S was lying on the ground, legs open and her knickers were on the floor next to her. M was kneeling between her legs and poking at her vagina. I called out to S 'Where's your mum' and she stood up and said she didn't know. I told her to put her knickers back on and she said that M had taken them off. I said 'ok, but put them back on now'.
They both ran off round the corner, out of sight. I was busy with dinner but ex-p (unasked by me) went to check on them again. They were doing it again and he called out and told them to stop.
I'm now really fretting about whether we've done the right thing. Have I interfered in something harmless? Should I have called the mothers out to deal with it?
I know curiosity is natural but I wouldn't have liked my DS to have been involved in this. I think I should tell one of the mums but I really don't want to cause a big argument and the 2 women don't get along at the best of times.
What would you have done?