Sounds like she's testing and wanting control back. Wanting to make sure you are still there.

I'd keep it short. Maybe something like:

"Sorry, I've been busy. If there's an emergency regarding the kids, I'd want you to call/text me. I'll make myself available when it concerns them."

M-33
W-33
S-11, S-8
M-11, T-14
BD - 12/26, Divorce Filing and admits to affair (her) 4/18
I moved out 5/23