Hey @Jackie2,
This has happened to me more than once where guests who made an instant booking brought in more guests than what my place can accomodate and gave excuses like last minute add-ons etc. In such cases, it wasn't the best thing for me to ask the extra person to leave, although I made it very clear that there's not enough space for them to have a comfortable stay but they insisted that they'd adjust and be fine. I didn't know what to do so I just asked them to pay an additional charge for the extra person which they did.
In your case, you have to options to deal with them,
1) If you are okay with the child staying, you can ask them to pay an additional charge for the child by making alterations to the itinenary.
2) If you are not okay (and it is absulutely fine to be not ok), then you can ask them to cancel their booking and mention that you wont be able to accomodate 3 guests. If they do not agree to cancel, involve Airbnb and get the booking canceled so that you don't get penalized.
I hope it helps 🙂
Hey Dave (@Dave-and-Deb0),
Are we allowed a one time instant booking cancellation without any consequesnce? I don't remember reading it anywhere, so just wanted to clarify. It's a very useful option if it's available.
Jeet 🙂