She added her mother and her husband had just spent £50k renovating their house, while she and her partner were struggling to pay the rent.
Parents on the forum reacted with outrage and dvised her to explain that she'd asked for help in the first place in order to save money.
Others questioned why she had taken the children out when there was food in the fridge.
One woman wrote: "I think you have to be honest with her and tell her you don't have the money as you weren't expecting her to take the children out, since you'd bought everything in at home for her visit.
"It's not fair that she made the decision to take the children out without checking whether funds were available."
Another mother advised her not to ask for help again, adding that she could find cheap holiday clubs in advance.
"I guess you will need to offer to pay her back in installments and then never ask for her help again," she said.
"Next time you are going to need to find other childcare - holiday clubs are sometimes cheaper if you book in advance."