so, my two both got new bikes for Christmas, what we forgot of course was to check that the little fingers could reach the brake levers - anyone know of some kind of lever extension that would fit between the bar and the existing lever?
You don't have to worry about this kind of things, 'cause kids can manage to shift levers which you'll see how they do soon.
On the other hands, you'll find handlebar for someone with short fingers, and supporting braking levers at your nearest bike shops.
If its a road bike, you could also do what I did with my daughters bike. Her reach was a little to short and also using the drop bar breaking system was new to her so I installed some suicide breaks the same as TT or Cycle-cross bikes use.
Its a great way to build confidence of a new style of riding as well as more safe for the little ones as they don't need to change hand position suddenly if they need to break in emergency.
Also as Allen correctly points out both drop bar breaks and standard flatbar breaks will have an adjustment screw to allow you to draw the lever closer to the bars and maybe located either on the outside or inside of the lever depending on type.