Most touring tires tend to be, as you put it, 'effin heavy', as they're built like a tank to withstand punctures and to have a long, long tread life.
and yes, worrying about another few hundred grams in a build with a spare seat and a kid is a bit over the top.
Just ride, man.
Slicks front and back are fine. I have often taken my race bike many many miles through rough gravel roads in the hills here on 21 mm slicks and lived to tell the tale. My wheels survive too, though the tires do get scuffed up a bit (Vittoria Evo CX tubulars). With sport contacts front and back you'll be fine, or with a tire with slightly knobby edges on the front if you go anywhere that's sandy or muddy or rooty (not the place to ride with a kid)...







105 and disc brakes! $35,000 sticker price! 