The family of a one-year-old is gunning to sue one of the biggest child care companies in the country … this after cops say their toddler tested positive for cocaine after being at one of their facilities.

B’Ivory LaMarr — an attorney repping Kimberly Hopson, the mother of the alleged child victim here — tells TMZ … the Hopson family plans to file a lawsuit against KinderCare Learning Centers for what they claim amounts to child neglect at the facility.

Hopson says her son was being looked after at a KinderCare in Oak Creek, WI earlier this month … where she suspects something untoward might’ve happened.

The reason … LaMarr says she got a call about the infant getting incredibly sick — and when she finally picked him up, she claims he had a bunch of bruises and abrasions on his body (including one in his mouth, we’re told) … which she attributes to the staff.

What’s worse, she says she took the child to the hospital and a battery of tests were run … and she claims the kid ended up testing positive for coke … something Oak Creek PD says in its press release over the incident, as well.

Cops say they were called for a potential child abuse case — and note that when the baby in question’s urine was tested … it showed he had traces of cocaine in his system. Officers say they conducted a subsequent search at the KinderCare facility itself, including sweeping the infant room, and they claim cocaine was found in one of the staffers’ bags.

That staffer was arrested on drug charges and a child neglect charge … but were told once it was kicked to the D.A.’s office, the neglect charge was dropped, leaving 2 counts of drug possession.

Legal docs obtained by TMZ show the daycare employee has been ordered to have no contact with the KinderCare location where the incident took place.

At this point, LaMarr tells us KinderCare has issued an apology to Kimberly and pledged to cover some out-of-pocket expenses for medical care — but we’re told that’s just not enough.

LaMarr says the family plans to sue the facility for negligence, negligent supervision, premises liability, assault and battery and potentially more … the general sentiment being, this worker who allegedly brought coke into the building should’ve never been allowed around kids.

The Hopson family plans to hold a press conference to further address this Wednesday. We’ve reached out to KinderCare for comment … so far, no word back.