Sorry this has happened.
I am not sure what your house rules say about keeping noise to a minimum, damage to your property etc.
But I think you need to take control. Have a chat with your guest and set boundaries. She is responsible for looking after her children in your place and ensuring they don't damage your property or disturb other guests or yourself.
If you have a limit to beach towels let her know there is one towel a week or whatever you offer and no further beach toys (she can buy these at XXX)
Folllow up this conversation on Airbnb messaging, confirming that if she would like to continue to stay, she needs to keep an eye on her children so there is no further damage to your property and her child is not disturbing others by their loud behaviour.
Also she needs to tell you immediately about any spillages and if she wants to have drinks in her room she needs to ensures spills are kept to a minimum.
Have you set up your rooms as 'family friendly'? Did she let you know that she had two children and the grandmother staying. If so what sleeping arrangements did you make with the guest rather this?
If she hadn't disclosed all the guests, you can charge for the adults and child over two in line with your charging policy and let her know she needs to accept the charges for her undisclosed guests if she wants to stay.
If she has brought more guests than have booked/don't improve their behaviour you can ask Airbnb to cancel the booking.