"train tracking"?

Helps train tracking and attention span.
I've seen that sentence a lot on the baby stuff.
What is train tracking?

Here, "train" is a verb, not a noun. Apparently, they are suggesting that babies, without their product, will have trouble tracking things.

"Tracking" is the ability to follow a moving object with one's eyes, which babies must develop. I guess your books are saying that there is a way to train babies to learn this skill faster.