So, you would only know this if you were at home, all day, watching them for 3.5hrs. I presume you watch her drop all of her children off at 9am, if you know there are older children?
Do you not work, or have anything else to do than stand at your window? Whom else do you watch?
Very odd behaviour. In fact, I would say it's harassment if you were to report this lady after approaching her already. Why was her csr running, so she could keep cool, bothering you?
This lady could be struggling for any number of reasons, she could just be saving herself some petrol by waiting 3.5hrs for the other children. (Please for the love of God do not say you know how far she has to travel, because that's extra stalkery!)
You just don't know. Unless the child has been abandoned, neglected, looks starved, or bruised - Stop spying on them! I work with vulnerable people and I seriously deplore people like yourself who make life so much unnecessarily harder for these parents and waste time. You will put a target on the back of a potentially innocent woman.
If she is struggling, don't kick her while she's already down. Her life really shouldn't concern you. Don't push her to some suicidal idiations because you think a Mum and baby parked in a car for 3.5hrs is illegal - It's not illegal.
Now, peel your nose and eyeballs from the window, polish off the marks, close your curtains, and go for a walk. Have a long hard think about what you're doing while you're at it.