something similar happened to us, robin, and it affected me much more than I thought it would. The actual amount of money was trivial, but it was a build up of little things and the attitude behind it that got me hopping mad.
In our case it was a neighbouring boy my son knew. He came from a large family and they didn't take him out much. It was no trouble for him to tag along with us to the park or to see a film etc. However, the cost of these outings, even if modest, soon built up and I realised I couldn't keep doing it. I knew his parents (though not destitute) didn't have huge amounts of cash so I didn't want to ask outright for contributions, but I nicely asked if the boy could have a little pocket money if he came on a day out with us. This was reluctantly supplied, but the boy never produced any money and the parents never ever said they would give me money direct for tickets, food etc even when they knew the trip involved me spending money. The boy would not offer to pay for anything - tickets, food or ice creams and I didn't want to make a big issue of it and insist every time. But at the end of the day (usually when I'd just finished saying 'no' to my son about having a last ice cream) he would run off and buy lots of sweets out of his pocket money, and then he would try to keep them to himself. I was in a no win situation, because I did not want my son to eat lots of sweets, yet I felt the boy should share what he had. He was 8 or 9 at the time so was IMO well aware of what he was doing. He really used to smirk about it. It wound me up so much, I stopped inviting him out with us. My son no longer sees him either - he says he's fed up with him, but the boy still knocks on our door.
Funnily enough my son's best friend asked to borrow £1.00 off my son today for a charity event. My son lent him the money and I am sure he will pay it back, and if he forgets, his mother will remember - I would have no qualms about asking her, but then I think she is a nice, fair person. I just couldn't do this with the other boy's mum because I didn't have that same trust in her - or as it turned out, in her son.