This usually starts because the puppy sees the nipping as welcome play behavior. Having toys is an alternative but only if the puppy gets reinforcement that any other biting chewing is not ok. You have to take a firm stand, that includes having the children issue a reprimand. Redirecting is not a reprimand, to your puppy it is just an extension of play. There must be a correction that will be remembered, a noticable nose thump, followed by a 10 minute period where all family members ignore the puppy is a place to start.