It's SIL birthday start of dec her bf is organising a surprise birthday gathering and has decided to go to a bowling type place. He told us about it in advance before paying a deposit. He thought it would be a good activity because our two DCs could also be involved. Will only be in-laws my Dh our dcs and sil and bf. They live 5 hours away so we will be staying over in a hotel. He has messaged today asking for us to transfer money to pay for the activity asking for £30pp totalling £120 and has asked that we also chip in for sil. I have phoned him to say that I am happy to pay for me and dh but I didn't realise I would also have to pay this for the Dcs as they are 2 and 4 and won't be able to do much. He's now really annoyed and said he can't get the deposit back and we had know the cost pp prior to booking. I had checked the package and it specified for over 18s so had assumed that it was not the same price for the kids- would I be unreasonable to not pay this? Mil thinks I should just pay it