I am divorced five years now, acrimonious split, felt quite traumatised and drained by it all. I was broke, so after a year of struggling financially I moved back in with my Mother who was a single mother herself and has been very supportive to us. She babysits the children if I need to be in two places at once, or if I have an appointment. But she's got lots of friends, she goes to the gym and has coffee &/or lunch with her friends or her sisters. So, she doesn't live to mind kids.
My mum introduced me to a neighbouring mother with children in the same classes as my children. This woman's husband is like something from the dark ages . If he has a day off he goes and does something on his own, golf, fishing, visiting his own family for three days without the children but when she visits her family she takes the children so he sits in the house on his own, quite happy!. She has asked me favours over the years and we have been friendly but not friends really. I just don't think we are similar enough and I haven't nurtured the friendship, even though I didn't mind helping her out occasionally.
Recently she asked me to go round to her house because she had the vomiting bug and she needed somebody to feed her kids. She asked me because she knows my mum looks after my children. Very reluctantly I went and looked after her children while my mum looked after my children. I got sick as did one of my children. I did ask 'Can John not come home from work then?'. I knew he wouldn't but I wanted to make that point that she should ask her husband first. she hadn't even asked him.
Then she asked me if I would mind her children when my children were with their father. so, on a day with no kids, I would mind hers? I pointed that out to her, that my own children wouldn't be around to keep her dc company, but she didn't get it. she didn't seem to immediately grasp why that made it a bigger favour to ask. Eventually I said, 'well if I have a child free day I think I'll go and do something fun! have a bottle of champagne". Made a joke of it. She said oh ok of course, but her body language told me she thought I was not very helpful.
Then she asked me to mind her younger son while she took her eldest somewhere. I couldn't help, so 
she asked me to ask my mother to look after my children so that I could look after hers.
I really don't know if I handled this like an assertive person or like a bitch. I said 'no. because I don't like to ask too many favours of my Mum, I only ask her if I really need her!!'. We then had a bit of a discussion that was tense but not outright rude. I told her the children's father and I were co-operating a lot more now, and kids and I were all looking forward to a fresh start in our new flat! (which is HALF the size of her house and not as nice, but she is not happy for us I suspect).
In my heart I know I did nothing wrong. This woman needs to ask more of her husband, and less of neighbours. But I have this feeling that she is feeling so martyred and hard done by.... because I won't help her!
Ok that was just a bit of a vent. I already feel better. However, our children are in the same classes and I'm dreading seeing her every day for the next year!!