The 10' Mana, although it's 32" wide, isn't all that huge. I'm 95kg on a good day, and have no troubles surfing it, it's actually amazingly very nice to ride. And as you can see in the below pic, with my 10 kg kid on board there isn't a great deal of board still floating out of the water.
However I haven't had the chance to ride the 9'5" yet, but I have heard it is pretty amazing. I'm pretty sure Sam has surfed both back to back, give him a bell a Windsurf n Snow.
JB