why has our cat suddenly turn violent

We have a male cat (neutered) just over a year old. He has been with us since he was 10 wks old and has always been very easy going - playful but never attacked anyone. About 2 weeks ago all of a sudden he started having these 'spells' when he runs through the house like crazy and started jumping at & scratching & biting the kids. At first I thought that maybe they provoked him but after watching them for a while I know that is not the case - they don't treat him any different than they used to.

He is an indoor cat, has his claws - I would never have those removed but I don't like him scratching the kids (even my husband, but never me) - just this morning he jumped on my 3yr old's back while she was just standing in the kitchen.

Why would a cat start behaving like this? We don't hurt him - so it's not in defense. Should we maybe let him out of the house (not very safe in the neighborhood though) to get whatever it is out of his system? What can we do with him?

He's a young male cat. Even though neutering him may mellow his manners in the long term, he's still young. I agree with other answers here involving spraying him with a water when he misbehaves. Also, put vinegar in the water, about a 1 to 5 vinegar to water ratio. Cats hate the smell, and especially hate it when the smell is on them. If he starts associating his attacks with smelling like vinegar, he's likely to catch on pretty quick.

He probably views it as fun, and isn't really trying to be mean, btw, so locking him in a basement is DEFINATELY NOT GOOD.