What would you do? Parents on drugs

So I’m a stay at home mom to a 9 month old and was looking to earn a little extra income. On Facebook I saw a family near me searching for childcare 2 days a week and they live right around the corner from me so I thought “Perfect!” I started watching their 7 month old mid May and it’s been going ok. Parents seemed great, baby just seemed cranky and unhappy a lot of the time but I figured it’s an adjustment period. Anyways, today she spit up all over her shirt so I went in the diaper bag to find a new one. I saw mom’s wallet in there and thought oh no, did she forget her drivers license and everything in here? So I opened it and found this... my mom works in law enforcement so I sent her a picture and her colleague said it’s either meth or crack cocaine. Unfortunately knowing this, I cannot watch their child anymore. The fact mom forgot it, what if the babies played in the diaper bag and swallowed it? My problem lies in, do I tell the truth or do I say I just got another job? Do I report it to the authorities? On one hand, I would never be able to live with myself if something happened to their little one because of the parents drug use, but on the other they are such involved and loving parents maybe I just keep out of it and let them work on it? I’m so lost.