One of my friends messaged me yesterday saying her DC has asked if we'll be seeing my same-age DC during the holidays (the DC are also friends) and should we arrange a get together for tomorrow. I said yes and suggested a local place we all like where we can get a coffee/hot chocolate and go for a walk. Friend agreed that would be great.
She messaged again today to check everything is still okay for tomorrow and would it be easier to meet there or meet at my house. I said we could meet at mine if she liked and have lunch here before heading out. Friend said that sounds lovely but she won't have time for lunch as she's at work tomorrow afternoon so will just be dropping DC off on her way there.
Nothing in her previous messages gives any hint that it would be me looking after her DC, I genuinely thought we were all going. I don't know if she's done it on purpose or if it's been crossed wires, she is a good friend (coming up 20yrs) but she does have form for being more than a bit disorganised so I wouldn't put it past her to have left it too late to sort childcare for tomorrow and to have resorted to this instead.
While her DC and my same-age DC get along, her DC is generally less tolerant of my other DC. They are very similar in personality so they get along initially but then they start to clash and repeatedly fall out. I know for a fact that friends DC being here all afternoon and into the early evening will be a trigger point and that I'm going to be constantly refereeing by mid-afternoon. My other DC is ND and will react massively to what they view as unfairness because they just want to join in and don't always recognise when they're not wanted so I'll also have to be managing them/their interactions and intervening accordingly.
I know IANBU to feel annoyed but how do I ask her if she did this on purpose or if it was a genuine misunderstanding without causing an upset? And if I do go ahead (if) how do I tell her that she needs to have words with her DC first about tolerating my other DC? She knows I already have enough on my plate with my own DC never mind accumulating extras.