I'm a regular here but have NC because this outs me.....
I am going on a 12 night camping holiday to France with a dear friend and my 6yo DS this summer.
Its booked and I've just paid the final balance which covers ferry and accommodation. The agreement is for my friend to pay their share in 2 weeks. Its through a camping holiday operator, it looks amazing but isn't as cheap as one might expect for camping (well I was surprised anyway 
).
When we booked the holiday I said that I would insist on on paying for my and DS' costs in their entirety. I assumed that this would probably amount to a bit less than 2/3 of the overall holiday cost (assuming that DS would cost less than us adults). I think my friend probably assumed this too, but we didn't actually agree on who was paying what.
Having looked at the invoice, and checked with the holiday company DS is actually completely free! We would be paying exactly the same amount whether he came or not (in fact we could take up to 4 DC and pay no extra).
So in a way, it could be fair to split the costs 50/50. This feels wrong to me though. Money is tight for both me and my friend, I don't want to pay more than I should, but neither should they. I want to be completely fair.
This friend has been my absolute rock, I owe a serious gratitude for helping me through tough times over the years. They seem as excited about this trip as I am but I can't help feeling extra grateful that a childless person would want to come away with DS and I, and I am conscious that holidaying with someone else's DC, when you are childfree yourself can be trying at times (I intend to minimise this as much as I can).
My friend is so lovely that I'm concerned that if I ask what they think they will agree to split costs 50:50, just to be nice while actually feeling that is a bit unfair.....
What would you do?