Ok, first a little bit of background...
Neighbours have 2 sons, 3 and 1 year old. Dd(4) is reasonably friendly with the 3 yr old. A few weekends ago dd was playing in neighbour's front yard. Neighbour mentioned that she was going to teach her 3 yr old to ride, and would dd like to learn too? Dd absolutely delighted- arrangement made for the following afternoon- neighbour would call for dd. Neigbours decided to take kids to beach for fish supper. Don't know if they invited dd, or if she invited herself, but they said she would be "no trouble", so I agreed to let them take her to beach. She had a great time (she said) and ate fried fish and chips 
BUT neighbour handed me a carrier bag with her pants in and said she'd had "a little accident". Opened bag once inside the house to find a HUGE poo! Next day, dd, all excited about learning to ride, insisted on sitting on step by front door all afternoon, clutching her cycle helmet. Neighbour did not turn up- I eventually walked down the road, and their car was gone. Horse still visible in field to back of our houses. Dd was heartbroken. There has been no contact from neighbours since, though her dh and me have waved at each other as I drove past their house. Don't know if neighbour was upset about the poo, or whther there had been a change of plan that was so sudden they couldn't ring to tell us, but I feel rather let down on dd's behalf, and more than a little cross with neighbour.
Anyhow....was driving down a main road yesterday, when I saw neighbour's 3 year old playing on a pavement! Am absolutely certain it was him, he looked up and waved as I drove past. he was with 2 other kids, I think are the neighbour's childminder's kids- both slightly, but not much older (oldest about 6 I think). Obviously, only saw the scene for a few seconds as I drove past, but on reflection I was horrified that the children were playing by a main road. This was during working hours, so suspect that they were outside the CM house...
Do I go round and say something to my neighbour? For all I know the CM was just inside the gate in the garden, for all I know, my neighbour was there as well, but really don't like the fact that the children were inches from a busy road. Don't want to be interfering (she has waxed lyrical in the past about how good her CM is)but, wouldn't want her child to be neglected, even if she didn't care about my dd's feelings.
What do you think I should do?