I think this needs to be sorted by the hosting parent.
Speak to them about the confusion. Ask them exactly what they booked - ie a career for how many boys and how many boys did she pay for.
If she paid for 2 (and other parent paid other carer for her son) then the carer has been fully paid.
If she paid for 1 (her own son) but then your son was there too, there has been a booking error on her part. In that case, the Carer would be expecting to deliver 1-1 care, but turns up to find 2 boys needing care (assuming 3rd cared for by other carer) and on that basis billed for it. She billed Op because she knows OP.
If this is the case, it was a booking error.
It’s impossible to say Op’s DS didn’t need care at all - he needs adult supervision of some level presumably.
In this situation, really the host ought to be footing the bill. They made a booking for care and then sent more teens than she had booked for, but didn’t pay. What did she think would happen - that the Carer would look after Teen 3 without charge? Did she think his own parent would be billed?
Why was carer wrong to charge for the OPs son, who is regularly cared for by her and spent the day with her. Perhaps the usual 2:1 rate is less than 1:1 but given. 2:1 doesn’t sound like it was booked for at all, I think the Carer could be irritated by this - not u reasonably.
So the problem sounds like it lies in the booking. Only 2 boys had carers booked, but 3 were there. The bill needs paying and Op needs to sort that with the host, not the Carer so much.
Imagine if this was a thread from the Carer.
‘My fellow Carer and I were booked for 2 teen boys on a day out, one being billed for each boy. On arrival a 3rd boy who we also care for sometimes turned out to be there too. We looked after the 3 boys all day and a good time was had by all. At the end of the day, we billed all 3 parents for the care their sons received. But now the one who was there but wasn’t booked in is saying she doesn’t want to pay for my services and hadn’t booked me. Is this reasonable to have received my services all day and not pay me’
This all comes down to poor communication mostly in part of the hosting family. Someone needs to pay the Carer. You’d hope the host will offer, having organised the day and organised carers without checking with Op. if however she doesn’t want to, I think OP should pay. Chalk it up to experience - communicate clearly in future.
And sorry, but son needing ‘almost no help’ in the day doesn’t mean that Carer doesn’t need paying. Looking after 3 teens is more work than 2.
It’s unfortunate this has happened, but it really wasn’t the fault of the Carer…they found themselves with more teens to look after than they’d been booked for.
Personally, I’d Id been them, I’d have texted the host and pointed out there were 3 boys and all 3 would be billed for. However, given all are known to them, simply billing for services received (and 3 boys were clearly there) seems reasonable too.