Mark,

a 45kg kid sailing this boat would be approximately equivalent to a 70kg Paper Tiger sailor in terms of the ratio of righting moment to heeling moment. While obviously not required I'd also encourage people to build a reef into the main sail so that the boat could be calmed down when required.

Where to next is a difficult question. I competed in my first adult Hobie nationals as a 45kg crew at 12 years of age on a Hobie 18. The obvious answer is a 14' boot (F14) but for most of these you'd want be at least 65kg so depending on the kid and the location you would either keep them on the 12 until they become big enough for the 14 or put them on a 14 and be willing to lock them in the car on windy days.

In the southern states of Australia I can see a very beneficial development being...

F12 --> Paper Tiger --> Mossie --> A cat/ F16