Do not make this about the daycare center. This is a horrible tragedy. I feel terrible for the parents, particularly the father who will have to live with this guilt for the rest of his life. But ultimately the fault lies with the father.
Most daycare places do have both numbers; however, parents have a tendency to take day off (particularly Fridays in summer) and don't always notify daycare.
I'm not sure the daycare people have the responsibility of tracking down kids in the custody of their parents.
Sad but sorry. I won't blame the daycare because the "father" screwed up. Daycare can never be "the parent" nor should it be. Very too sad for all involved, but the blame rests on one sad person's shoulders.
Spoken like a plaintiff's attorney - even down to the yelling.