6 years old!!

So I need yalls help!!! This little boy lives across the street from me and he’s 6 years old ok well he gets off the bus from school at 3:50 everyday and goes into a house that there is no one in!! ( I only know this because I used to be his babysitter but I got a job so couldn’t watch him anymore) well when I look outside no one would be home for more than 3 hours!! I’ve recently quit my current job because I had miscarried and was to stressed out and asked if they would let me baby sit for them again and they said no that he can stay at the house by himself!!! He is 6!!! What should I do? Just leave it alone or call CPS????