Being an old(er) player, my teams have often had young players on the squad. A couple of things I've found helpful in convincing parents to let the younger players travel for tournaments and such...
- Get to know the parents. Talk to them (at least a "Hi, how are you?" when you pick up little Johnny), let them know you're not a deranged survivalist freak (I'm assuming you're not). Parents are much more likely to trust their precious offspring to someone they know. Don't forget to mention things like how safe the sport is, how popular it's becoming, etc.
- Invite the parents to come out to practice or a local tournament, so they can see what you're doing and they understand it's a sport. Even if they don't show up, this will help them see PB as a legit activity. If the parents take you up on your offer, try to be on your best behaviour and watch the cursing, arguing, etc. Show them that this is a positive growth experience for the kids.
- Talk about the positive aspects of the sport - teamwork, building communication skills, developing self-reliance, etc. If little Johnny is doing something to earn money to pay for his expensive new habit, that's even better, as it shows he's developing the maturity to handle money and commitment.
- Show a commitment to the sport. If little Johnny goes to practice every week, it shows this isn't an excuse to go party or a passing fad. See the point about money too.
Don't expect parents to just hand over their kids on your word. You need to show them that you're serious about the sport and you can be trusted to look after their child. Finally, don't forget that if they do trust you with their kid, you have a certain responsibility to watch over them. Make sure you're willing to accept that responsibility.