A) it wasn't an infant, it was a toddler. Toddlers can be pretty quick B) the fence was not substantial, a toddler could easily walk through it (and did); then there was a couple feet of ground until the slope down to the moat. C) the mom had more than one child there. D) it's not socially acceptable to put leashes on children (except for the cutesy backpack ones, but that's not really going to help)

The gorilla enclosure was built to prevent the gorilla from getting out, not to prevent people from getting in.

Edit: Before and after of the fence https://www.dailywire.com/sites/default/files/uploads/2016/0...