The reason for the 1020 or 1520 was 41MP or 20MP of pure beautiful picture (matching and sometime surpassing many PnS cameras out there), with the armour, it make the phone much more durable against knocks and drops. And with the 1520, it had plenty of juice in it.
So... that should be one of the best choice out there.
I dont think a 5yo kid will be into the technicality of a camera. If anything its the composition of photos, capturing of moments that's gonna get him interested in photography. Any camera with a screen or vf and an auto setting would do imo.
Another thought, you can trick out any cheap PNS (Canon PowerShot A1400 looks like it'll be easy for kids to hold, with its beefy grip) into a 'drop proof' camera by adding bumpers with SUGRU. Imagine it could be an activity in itself if you can get your kid involved in the customising process.