1. Your Kid has a proper bike to ride - so he can go out riding with you.
2. The Better Kids Bike - if looked after - will hold it value well, so much so something like this Kona 20 could end up costing you less than a cheap bike when you come to sell it. A good few years ago my buddy Tim bought a Trek Mountain Lion for his lad (not dissimilar to this), it got plenty of use over a few years then he passed it onto me and my lad who was a couple of years younger used it - then my youngest lad used it. Over that time it was looked after, Tim fitted an older XT rear mech that he had "in stock" and the bike kept going and going. It had rigid forks and V-brakes which was the norm at the time but it has good components. From memory it cost about £225 in c1995 - after going through 3 hands we put it on eBay and it went for £180 IIRC. That works out at less than £10 a year depreciation for the 5 or so years we had it... less than the cost of a heavy supermarket bike.
In stock now (it comes in a 24" version too).
£379.99 including free UK delivery.