Really concerned

I don't sleep well at night since my 7 month old wakes up quite frequently so I usually get up and get a drink, well last night thats what I did at 1:30 and this is what I witnessed. My neighbor who I babysit for racing around town in her bf mustang. I know not that big of a deal. The car is very loud so after a few minutes of listening to it I got up again and looked and the mom was on the porch going inside then coming back out and getting back in the car, they left and went up the road but it was a road that was recently washed out so I was a little curious (nosey) as to where they were going. They came back 2 or 3 minutes later with construction cones sticking out of the sun roof and continued cruising up and down the roads with no real purpose for over 45 minutes. This is why I am concerned, mom picked up kids from me yesterday, today is youngest daughters first day of school and mom to a half day to get her off to school. I may be jumping to conclusions but mom has gone through a definate change since seperating from dad and I wouldn't put it past her if she got drinking to think leaving her two daughters by themselves while they drove around town was ok. I think I am going to ask dcg when she gets here after school who she stayed with last night just incase dad came to pick them up for some strange reason, but if she says mom what do I do then? They are 6 and 3 and that is just ridiculous. I worry about these girls constantly. I asked older daughter if mommy was sad that her sister was starting school and she said no mommys happy because she doesn't want to deal with us because we are getting crazy because there isn't as much to do at mommys as there is daddys. I really hope I am wrong, I have to be what parent would do something like this.