I got one of these although it was discounted from this price at the time.
http://www.evanscycles.com/products/hamax/smiley-child-seat-ec007574?query=child seats
Decent quality and relatively east to fit, although as it goes onto your seat tube you do have to watch that you don't have cables running down the seat tube as I do on my giant XTC. Still managed but fit it on but I lost my front mech control (don't need this at centre parks anyway). You can, I think, put them onto your seat post but may end up with a very high child seat that would really raise the centre of gravity quite high.
All in all a good buy, although the one above looks a better bargain at the moment - plus it looks a bit cooler.