We had both of our grown kids and six grandkids at Lake Hartwell for Memorial Day weekend.  We are encouraging the older grandkids to experiment with boarding and skiing, but they always seem to gravitate to the tubes.  While the skill required is lacking, the fun is being able to have a group of people all riding at the same time.   We have been using these Airhead 3-person tubes for several years.  I like the size, and we can usually get at least one full season from them with pretty constant use.  The fun goes up exponentially with two or more tubes.  We don't have our video assembled for this year, but this one from last year gives a good feel for what we spent hours doing Memorial Day weekend.