Bruising to the top of his knees would make me suspect he may be banging them kicking in the highchair when he is ready to get down but they are not quite ready for him or it is taking a bit longer to get his food to him than he is used to.
Bruising to the bottom of knees would make me suspect crawling on hard floors or dropping back down from standing at the toy shelves.
Both would be common bumps and bruises that most group providers would not really take notice of as they are expected.
The small mark under his eye could be from learning to use a book for the first time, pulling a toy from another child that gave way sooner than he expected or even faceplanting in the toy box as is pretty common of wobblers.
I'd look for the most likely scenario before assuming malice. We are not required to record them unless they require treatment or the child was visibly upset and injured. Most kids don't even notice the small bumps and bruises unless we make them.