RE: Rigs for Kids
Without actually seeing your daughters and their skills, I cannot say for sure, but we've had students (100's of them over the years) as young and small as your youngest (and many that were probably younger and smaller) who did quite well on the Retro Ripper 2.5 and 3.3 m2 rigs. Both of these sails rig on the Sailworks 310 RipStick RDM and are as light as possible without sacrificing durability and tuneability.
Thus far, of the people I've recommended the Retro Rippers to, no one has come back and said they didn't like them and most have had nothing but praise for these rigs as they provide alot more power (and performance/speed as soon as your fledgling sailors can handle it) than the less expensive and flatter kids rigs.
A number of people have purchased other less expensive kids rigs and gotten their kids started in the sport on them, but have ultimately purchased the Retro Ripper in appropriate sizes and seen an immediate
improvement in their kids skill levels.
The Retro Rippers are simply downsized Sailworks Retros (for the most part) and they teach new sailors how to handle power in the rig right from the start.
Other rigs, that don't have as much power, may be easier for the first 1/2 hour or so, but beyond that, they don't provide a good progression, either in skill level or ability to sail in stronger conditions because the new sailor has not had to deal with very much, if any real "power" from the rig, so as soon as things power up a little they have problems.
With our "A Taste of Windsurfing" program, our students already know how to handle the power in the rig, from their 5-10 minutes on the simulator with Ellen, as well as how to uphaul correctly, keep the board an rig in alignment, get the rig across so it balances, how to "rotate" the upper body to add forward drive from the rig, and how to dump or reduce the power if it becomes too much for them.
Then I take them on the water and virtually all of them sail off, with me on the front of the board or on a tether right in front of them, with enough skills to sail across the wind, tack and return across the wind to where they started. This is in their first 5 minutes on the water.
So, I've become convinced that having a small lightweight sail that balances well and provides good progressive power characteristics is actually easier for them to learn on than a flat limited power rig, or a
floppy old style trainer rig where the power moves around alot.
If you are anywhere near Rhode Island, perhaps you can hook up with Ellen or borrow her 2.5 and 3.3 for a test drive with your girls.
I believe Ellen also has a Starsurfer.
Other than inviting you and your girls to come to one of our free "A Taste of Windsurfing" events in the spring, there no absolute "for sure' way to tell which size rig (s) you might need.
The real criteria, from my experience, is their ability to uphaul a rig of a certain weight. Learning to uphaul correctly (using the larger thigh muscles rather than the smaller muscle groups in the lower back and arms), seems to help the "little ones" sucessfully uphaul larger rigs than we might think them capable of.
Once the rig is out of the water, they can balance it, and the weight is no longer an issue.
And, if they have learned how to "regulate" the power (through sheeting in and out, as required, to keep the power steady and manageable for their petite size) they can progress very rapidly.
Their progress, and the ease with which they sail (as long a things stay balanced) will simply astonish you.
They will be ready to do things it took you as an adult days or weeks to pick up, in a couple of hours.
Hope this helps,