+1 to this suggestion. - if we knew where you were located or looking to sail, we could narrow the suggestions down a bit.
having said that, have a look at this video on Sabots....
I should declare a vested interest as my daughter sails one.
the class is raced with two crew (2up) to the age of 11 and then 1 up from 12, with 11 being a transition year.
if you are anywhere near lake Macquarie around new year from 28th - 3rd, the sabot national championships will be on at Wangi with about 120 or so boats expected.
the national website will show you at what clubs they are sailed (mainly east coast & tas).
the important thing is to get them sailing within their own age group with a class / club where there are a few of the same class boats that you choose, the kids will learn off the other kids, have lots in common and there will also be knowledgeable parents to help with setup etc.
for my 2c worth..At most clubs you will find that lasers and Sabres are sailed by older youths and adults. some of the bigger boats might be alright if they just want to muck around or if you want to sail with them off the beach somewhere, but you said they were keen to race, so they need to be in a boat with rules that allow 2 up (not lasers or sabres) unless the club modify the rules to allow it for juniors.
Flying 11 is an awesome boat, but not for a 10yo starting out. - manly junior might be more appropriate, but that class has contracted a fair bit over the years.
They will learn and develop much better in something that they can manage. and after a few years in a sabot or opti, open bic, PJ, MJ etc, the F11 would definitely be worth considering.
BUT, if all you are wanting is to get them on the water to go for a sail, then ebay is your oyster (& caveat emptor !!!!).
and while I am going....whilst YA & YNSW are pushing the opti and "pathway" programme hard, we should ask how many aussie gold medallists have come out of it ? most of them came up come thru sabots & F11.
getting down off my soapbox, now....
good luck