Your XW should have let you know that she wasn't taking him to daycare and yes, that was stupid of her not to, but that's where the fault ends.
I respectfully disagree. This was not "stupid" nor is it where the fault ends. It is unacceptable and irresponsibly neglectful and deceitful on her part. Child Protective Services, buffet. That and/or a strong, iron-clad, no B.S. Boundary on this!
Gardener
"My soul, be satisfied with flowers, With fruit, with weeds even; but gather them In the one garden you may call your own." Cyrano deBergerac