In theory, I would say a toy guitar is very fun and very educational--but not the Bontempi model. We gave this to our son for Christmas, and the bridge broke into two pieces that same day, while I tried to tune it. The bridge is made out of balsa wood, which means it can't withstand even reasonable tension without breaking along the holes where the strings are tied.
The toystore where we bought it was nice enough to exchange it, but the same thing happened to this second guitar. I had even coated the bridge with superglue (which is probably why it lasted 4 months).
Now we'll buy a real ukelele--enough with these toy guitars. I can't tell you how disappointed our son was.