I'd say you should reconsider.
I owned a Fun1 but probably didn't get a great value out of it because it was really only used in flatwater. By age 8, my son was ready for the Fun 1.5 and we've had much more real use out of it as he's actually big enough and strong enough to paddle it in some easy whitewater. He'll be 11 this year and it might be his last year in the Fun 1.5.
The years go quick. Unless you're trying to have your youngster paddle real whitewater, I'd say let them paddle the 1.5 and by the time they're truly ready for real paddling, they'll have grown into the 1.5 size anyway.
Just my experience and two cents.