I say trigger all the way! Though I've never used a high end grip shift, I have yet to meet anyone regretting going straight to trigger. As opposed to the other way.

 

Take your little-un to a bike shop which has bikes fitted with both and see how they get on.
When we did that we found our little-un didnt have the strength to turn any of the grip shifters.
She was able to use the triggers (just).

It all depends on:
a) wrist/thumb strength
b) the rest of the components
c) how the springs are set up in the mech

 

For both my kids grip shift was horrible. Trigger were much easier.

 

My kids were just the opposite. With the grip shifters, they were able to use the larger muscles in their arms, versus just the finger muscles for the triggers. It all depends on the kids motor skills

 

My 7 yo son was having trouble with the low end grip shift on his 20" GT Aggressor. It was some very low end Shimano twist shifter with a low end Tourney derailleur. He had to completely twist his arm in weird positions to get it to work, not very safe. Switched to a SRAM x.5 trigger and derailleur and he shifts now with no problem whatsoever. One of the best, cheap upgrades I made on his bike. High end X0 Grip Shift may be better, but the low end stuff that comes stock is terrible.

 

OK thanks guys. I like the idea of taking him to a shop to try out the different shifters. I'll definitely do that. I'll keep updating on what I figure out.

 

my 6 year old loves her trigger shifter she ad alot of trouble down shifting with the gripshifter wich is your most importent shift,none now that I swapped it out with triggers

 

My daughter had trouble getting the grip shifter to move, and then would overshoot when it did. Had no trouble when I put on the trigger shifter. My son has had no issues with the grip shift on his bike. I think it mostly comes down to hand strength, but his derailleur may also be a bit smoother.

 

So it seems Trigger shift is the way to go. I'll see what my little guy does best with at the bike shop.

 

Gotta agree. Trigger will make riding much easier.

 

I say Trigger is best. Especially Shimano products. The shifting ratio used on the Shimano is way better for kids than the Sram products. Every Sram build I have done the dads say the kids have a hard time shifting gears. I have yet to have a dad complain about the kids shifting Shimano gears.

Cheers