Sailing out of Boston-30ft+
I too have a 7-year old child who I hope will take more and more interest in sailing as he grows. I recently acquired a Peterson 34 which, as JeffH says, is a close relative (in design, at least) to the Contessa 35. Jeff is right that there are other boats that may be more seaworthy, offer better motion comfort, and/or be easier to single-hand, but that does not mean that these boats are not at all seaworthy themselves or couldn''t be single-handed (for the latter, a lot depends on how they are set up). Boat selection tends to involve a lot of trade-offs, including comfort, performance, price, etc... The Pearson 323 and Tartan 34 represent different trade-offs than the Contessa 35 or Peterson 34.
Successfully taking ANY boat out in 45 knots would require experience, proper sails and equipment, and intimate knowledge of your boat and its condition. I would be a bit reluctant to do so with my boat in her present, 25-year-old raced-hard put-away-wet condition (Jeff has seen my boat) but I hope to have a lot more confidence in her after a full overhaul and refit.
Back to my 7-year old son, on our first trip with our "new" Peterson 34,he kept his eye on the heel-o-meter and was quick to bring it to my attention whenever we got above 15 degrees (see http://members.acadia.net/catamount/Greyhawk/reaching.jpg) -- that was until he found a secure place where he could wedge himself (in the deck-wells where the MOB horseshoe buoys would be stored); then he forgot all about the heeling!