It's not entirely out of the question. Minnesota law for neglect says the following can be considered under neglect: A parent, legal guardian, or caretaker.
Caretaker as defined under 609.376 means an individual who has responsibility for the care of a child as a result of a family relationship or who has assumed responsibility for all or a portion of the care of a child.
He himself admits he was being a maid for them - cleaning, cooking sphagetti-o, etc while spending an insane amount of time in their home.
There's also the fact that he was aware that drugs were around his own children for months. Do you think Nick wasn't giving April stuff to take home?