Yes. The sprouts are coming up off of the old tree's roots.
Kill 'em. Or else you will get a jungle of black locust trees
that will be covered with nasty thorns.

The thorns were 2+" long, solidly attached to the branch, sharp as a stiletto, and I would swear had toxin in the tips.

The city usually mows them down but hasn't because of storm cleanup. It looks like a little forest.

I think they are honey locust with long vicious thorns. If you cut them down they will send up suckers (sprouts) from the roots of the parent tree. They are horrible. My cousin killed off a lot of them and mesquites as well using a powerful herbicide that is applied to the trunk. I got ride of a lot of them by cutting them down and letting my goats graze. The thorns on spouts and new wood are rubbery at first. The goats just loved them. Eventually the stumps rotted and I was able to just kick them over.

If the stump of the parent tree is still viable you might be able to have it professionally treated with whatever that chemical my cousin used. Hopefully your neighbor will go along because they are all over his yard as well. One other thing- mow them down consistently while still young. Eventually they will give up.

I have another neighbor who has two goats. Maybe I will ask if they would like to visit. Otherwise, I'll get out the mower. I can't believe how many there are.

I love them but they will eat most all of your shrubs, and they will jump on your vehicles to reach low hanging tree limbs. There is a reason that young goats and children are both kids.