to think that you should supervise your toddler child in the park rather than stand and have a smoke

[xxxresixxx]

As above. Mother with DD who was about 2.5. Mother stood at far side of park having a chat and smoke with friend completely oblivious to what her DD was doing. DD was other side of park playing. When my DS who is 20 months approached her dd, the dd grabbed my DS and sink her teeth into his ear (only not his face because DS turned his head). DS inconsolable with still visible one hour later bite marks on his ear. Woman didn't notice and only reason I know who the child mother was was because I tools the child to tel me who mummy was and matches over. I told her what happened and the response was a shrug and a comment about all toddlers biting before saying to the little girl that she had told her not to bite. I may have given a piece of my mind about the quality of her parenting/duty to supervise her young (and berry child) and the fact anyone could have walked off with her DS and she wouldn't have noticed. I got told to fuck off which didn't surprise me but Aibu?

what tailtwister said.

Yeah sorry, helicopter parent my arse. They need supervising!! Why should another parent watch yours as well? which is basically what you are asking, if you fuck off to a part of the park where you can't see your child.
I smoke,and i have stood outside the railings and watched my kids, only when v. desperate, as can't cope with the looks!
But i wouldn't let them out of my sight, certainly not if they were biters, it's YOUR responsibility to do what you can to teach, guide and prevent if possible.
Saying all that, I don't know what your attitude to her was, so you may or may not have deserved the fuck off!