Skip 26-inch racket and move directly to 27-inch (adult size). 26 is very similar to 27 and waste of money.
Sometimes I would have players skip the 25" racket and go to the 26" instead. My feeling is that most junior frames are waaay too light... esp those cheaper aluminum frames. My belief is that players should play with the heaviest racket they can comfortably swing, not the lightest. Easier to develop proper stroke mechanics with a heavier frame. And usually less frame shock -- esp if they sometimes play with standard tennis balls (as they often do it when hitting with adult players).
Unfortunately, the grip size available on many 27" rackets is a bit too large for small hands. Grip size on 26" frames is 0, just a scosh larger than the 00 for 25". But, in a lot of stores, it has sometimes been difficult to find anything smaller than a 2 or a 3 for 27" rackets. I believe that grip 1 frames are available, for some models, online. But sometimes you have to wait longer for those to come back into stock.
I would suggest that players try to find the heaviest 25" or 26" racket they could find... preferably 250 g or greater (unstrung). Even this is a bit too light.