Not to belittle your suggestion Col but the GoKeys costs more than 50% more than the CT-X700 and plus I don't think the extra bells and whistles are a distraction for young players but rather a way to keep them interested in the instrument far longer than simply having to hit the right keys in the right order day after day after day.
To be honest, if you really want to get your child to play proper piano style in the hopes of nurturing a young Rachmaninoff then you're better off looking on your local craigslist where at any given time there are dozens if not hundreds of acoustic pianos looking for a good home for nothing more than the cost of hiring a piano mover and a piano tuner to set it up once it arrives.
Plenty of people out there own acoustic uprights which they are willing to part with for the cost of hauling it away.
Since the child in question is 5 years old I presume he or she will not have unsupervised access to the board anyway.
After a 45 minute practice session of scales and chords, the funky sounds can be offered as a small reward to the child to allow them to cut loose a bit and have some fun.
Otherwise I fear that after a year or two of lessons the kid will become bored with the limited sounds of the GoKeys and end up relegating it to the storage closet.
Just my thoughts on the subject.
Gary
