I'm sat in my bedroom with the window open and heard the child next door (aged 3) giggling, followed by her mum with a raised voice/through gritted teeth say "get in, get in now".
There was some more giggling as I think she was running away from her and I then heard the sound of a smack and the child said "ouch" and started crying. They then went in.
Friend thinks I should report. I've not had any concerns prior to this.