ok I will chime in
it does depend on the age of each kid of course, and you can have them bowling without being in a league
my son started in a bumper league @ 3 1/2 he bowled that for about a year and I noticed he was starting to throw the ball 1 handed, and he is kinda small/skinny mainly not hieght.. but after a half year on bumbers throwing 1 handed i noticed he could avg about 60's with 1 hand and no bumpers, so I moved him up to the actual league and for his half season he avg'd 71 I think and he bowled youth state with some of his bowling friends he had already, and family tournament which we went to the state part of it which was kewl for him, and he qualified for the youth missouri olympics by bowling descent in state LOL.
this year he was a little stronger and about half way in he moved up to a 8 pound ball, and doing alright now he is up to about a 85 avg and having fun, he is also left handed, so drop ball around 1st arrow and over hook the lane with a vizaball LOLOL without really trying to throw the hook, at times he tries to force a hook already from seeing other kids doing it, and have to remind him that he is doing ok if not better then some of them and he is about 3-4 years younger then most of them lolol
@ start of 2008 my daughter started bowling in the bumper league and she is 4 but she is really tiny, and she will prob bowl there for a few years with how small she is before she could throw with 1 hand...and get it down without bumpers then I will move her up of course
so just enjoy it, and more they are @ bowling alley when young the more they want to do it, I noticed
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current arsenal
Morich Ravage (4 sale)
Morich Shock & Awe
Morich Awesome Finish (4 sale)
Morich LevRG
Roto Grip Odyssey
Roto Grip Quest
Roto Grip Cell
Columbia 300 Piranha/c Pearl (old school
)
Ebonite SR300 (4 sale)
Brunswick vizaball Ichiro