When you're buying a guitar for a child, i think there are a few important points to consider. One, don't get anything too expensive, as it may get earthworms, bits of toy, and tantrums thrown at it. Two, get something that actually sounds good, otherwise said child may just get frustrated and give up. Three, i think it's important that although the guitar is small enough for the player to handle, the fretboard should be normal in scale- ie, the frets are the same distance apart as in full-sized guitars. My little brother had one where they weren't, and his poor wee fingers got discombobulated when he tried to play a full sized guitar.
It might be better, if you can, to get a small travel guitar intended for adults, rather than one intended specifically for children; they're less toy-like, but they may be expensive and prone to breakage.
Good luck! :)