I built up a custom 20" mountain for my son last year when he was 5. I ditched the gripshift for a couple of reasons. Firstly they were really hard to twist around particularly when going to the larger rear sprocket even though they were easier to change back to the smallest sprocket. Secondly I decided to upgrade the whole gear set to a nine speed and had an old Deore LX STI trigger shifter so used that.
My son found the trigger shifter easier to use than the gripshift even though there is a bit of free movement in the thumb lever before engaging the click. I was thinking about replacing this with a newer XT version as there isn't as much free play before it engages but he's fine with it as it is.
As said before kids don't have a great concept with gear use so I used a 1X9 drivetrain so he could get used to the shifting before moving onto 2 or 3X systems. As it is everything seems to be moving to 2X and 1X anyway. He has learned to use them but quite often I still have to tell him to change when he's spinning too fast lol.
At the end of the day like us the kids will have a preference if they have a choice. I've personally never liked gripshift and have always used trigger shifters.
Also if you are planning on disc brakes the newer shimano brakes are great for little hands.
He's a picture of the bike I built and painted for my son from my build album on Pinkbike.
That is rather inspiring - and I cant help but wonder what forks you have on there? I was thinking rigid as all the forks I can see are just horrid crap and heavy, so what you got on there?
That decal position makes the lowers look bent though!
I did check out a Carrera blast with revoshift the other day in Halfords and was pleasantly surprised but its ease of use.
Think no gears is best for now though, doesn't use the bike enough to figure out rapid fire!
The forks are spinner air forks and they are reasonable forks for the price. They don't have a lot of adjustments but you can adjust the pressure for weight and they also have lock out. Yes the decal placements do make the forks look bent and I have been meaning to make some stickers for them.
I got them from www.bluepill.pl who are the European distributors and are based in Poland. I got them for about £65 when the pound was quite strong against the Euro last year. If you do want some the contact details are below.
Lukasz Nowak
SPINNER EUROPE
Ul. Gdanska 112, 90-508 Lodz, Poland
Email: lukasz.nowak@bluepill.pl
Mobile: +48 605 607 358