Well there you have it... 6001RS
That's all you need to get the exact same bearing as was in it.
It's a 12mm I.D. a 28mm O.D. x 8mm wide sealed both sides.
McMaster Carr is selling them for $6.97 each
http://www.mcmaster.com/#5972k82/=cdgpqg
These will handle a radial load of 1,150 lbs. and a max. of 18,000 rpm. So unless your kid is really fat and you can run like the wind you'll be in good shape with this bearing.
Like has been said... FORGET the ABEC numbers. This is a stroller, not a spaceship.