It makes sense to me, they got a report for possible child neglect and drug use, asked CPS if there was an endangerment problem with the kids, CPS said no not legally, and therefore the cop very specifically asked to look for the drugs and only the drugs. The warrant application doesn't really go into the kids apart from mentioning that there was a report of them being smelly and possibly neglected, which is just a fact, and also a sign of druggie parents. He then lists all the other stuff that signifies druggie parents, or Nick in particular.
The cop only asks to look for drugs and doesn't talk about child neglect as the crime at all. That's just gravy because guess what, being white trash drug addled parents fucking other white trash fucks up your kids.