We used not-to- tall book shelves, with first shelf placed higher than normal, and we bolted the top of the book case into the wall behind with heavy duty wire so it couldn't tip over on anyone.

TV's are a big problem with toddlers/kids.

I haven't seen any where the bracket locks into the track. Get the kind that screws the shelf into the bracket and where the bracket for sure.
I wouldn't do it with a toddler unless the lowest shelf Is way high up and to high to climb on.

I am too cheap to have real bookshelves installed and thinking about track shelves. I am worried about my toddler climbing on them and pulling a shelf down and on to himself. Has anyone installed these before -- how solid are they if done correctly? The track would be secured to the wall with screws so I am not too worried about that - more about how the bracket secures to the track.