Shouldn't be any of it, imo. I'm Pres of a local cricket club and it's a blight on the game and should be punished in junior ranks. Our associaiton has brought in a rule in juniors and seniors of zero tolerance for bad behaviour including sledging (it is policed with common sense though - the umpires tell the captain that their player is going too far and the captain has the option to do something about it). If the player goes on with it they are reported, and here's the good bit - if the player is suspended, so is the captain and the team loses 5 competition points.
It's an attempt to stop what happened a few years ago when, in the middle of a heated argument, one fielder ripped out a stump and tried to stab the batsman with it. He got a life ban, although he may still open the bowling for the Long Bay Gaol XI.
The solution is simple - tell the kid to shut up, and if he won't make him run from fine leg to fine leg for the rest of the day and see how he likes it.
We all know that adults do it and the kid are emulating them but is sh*ts me to tears, frankly. It's embarrassing to see kids who barely come up to the bails abusing each other or just carrying on like pork chops.
I'm no wowser in general, but seing kids sledge is just a real bad look imo. On the weekend I was coaching my 5 year old at soccer. He asks me after the game "Did we score more goals or did they?" "They did". "I hate them, Dad". Surely a potential Aussie Test cricketer there!!! I had to explain to him how it's not right to be like that, and I think he got it. But kids by definition are immature so if they are allowed to sledge their comments will be puerile at best and vicious (as kids so often are) at worst.
As for me, I generally dont have anything to say on the field, unless someone says something to me 1st, then all bets are off. But you tend to get away with a lot more when you've been playig for 32 years and all the umpires know you. Double standard I know, but that's the way I feel about it.