Far too many. It's likely these abandoned children will also become more feral over time as well. When Yugoslavia collapsed and fell into war, there were children roaming the streets and adopted by dog packs. Some had been orphaned or abandoned so young they never learned to speak or walk properly.

We're not in a war situation here, but that's an example of exactly how badly feral children can regress.

The Tarzan stories are not an accurate representation of feral children.