A lot of those cheap $10 are crap that I've seen.. They're ok for a small child but once they get to about 8yrs old they will need something better.
You can go down to Canoes Plus in Kew (Melbourne) and pick up the bits you need to make a decent paddle.
They have the black anodized alloy tube.
Also good quallity paddle blades and T grips.
They will cut it to the length you just need to tap the T grip into the end and the same with the blade.. No screw or rivets needed.
It could be made in a few minutes and only cost about $50.
Bargan!... I just live up the road and can meet you there if you need a hand.. I've made half a dozen of these and they work well.
The next and best option is to go for one of the new Kialoa adjustable paddles.. They are a pretty good price and you can adjust it as they get older/taller.
Here's a link..
www.seabreeze.com.au/forums/topic.asp?TOPIC_ID=46003&SearchTerms=Kialoa,adjustableYou may even like it enough to use it yourself.
DJ