Classic toys that are made well remain popular again and again. Nerf toys are fun because they are safe. They satisfy a basic thing that all kids like to do, which is to play tag. They are harmless. They get kids running around. For these reasons, Nerf will stand the test of time.
Children love to play all sorts of games, and especially boys who love to shoot each other with toy guns. This doesn't mean kids will grow up to be violent because they had a Nerf gun. Huge amounts of children have them in the UK and gun violence is incredibly low in Britain. There are other factors that cause gun violence, blaming Nerf guns is pathetic.
Yes, Nerf guns will likely remain popular with future generations of children. Kids naturally like to play games of attack, and guns provide an opportunity to do that with the added benefit of aim an shoot. Nerf provides a safe way to do this (no getting hit with sticks or rocks). The popularity will likely continue until another similar technology emerges.
No, NERF guns will not remain popular with future generations of children. We are living in an age of unprecedented large-scale gun violence. Parents do not want to encourage their children to shoot people, even if it is with a relatively harmless NERF guns. I expect these items to lose popularity.