Kids are book writing catalysts for some reason. They open your heart to the bigger picture in strange ways!
From my own past decade of parenting, I’d say - WRITE IT NOW! Because about 2 years from now you’ll enter the phase of life where no thought, no conversation, and basically no other activity you ever do - goes uninterrupted.
I’m not surprised you got offered a book deal. You’re a highly readable, and very altruistic writer.
Best luck with the project!!!!