At our house, chores are approached casually and happily, with everyone pitching in. When it came time to start work on our renovation, we kept the same attitude, with everyone contributing according to his or her ability. Some of us install new plumbing, some paint, and some hammer their little hearts out.
Just as we do when it comes to chores, we maintain realistic expectations. We would never expect a kid to clean a bathroom as thoroughly as an adult would, or sort laundry carefully, or demo a bathroom, but we do want him to be involved and to feel proud. Though the three of us don't usually work on the new house together, the times that we do are particularly sweet. Here's what the 7-year-old has crushed so far:
Sweeping: There aren't too many ways a kid can screw up sweeping, and the thing I'm learning about renovation is that there's always sweeping to be done.
Sanding: Detailed sanding can be a tedious chore, but we happen to have a few sanding jobs that don't require too much detail-oriented work. Lightly sanding something so it can be repainted (in our case, an old vanity) is a great task for a dust mask-wearing kid.
Carrying things: Energetic little legs can put a serious dent in the millions of trips in and out of the house that need to be done: carrying small things to to the trash cans by himself/herself, helping to carry larger items to the dumpster, and feeling strong.
Vacuuming: I know a few kids that love to vacuum, and getting to use the R2-D2-like Shop-Vac is a treat. It's cool in the same way earth-movers are, all black and yellow and heavy-duty!
Collecting nails: I was in charge of removing the double sets of trim around the base of the walls using a pry bar and though I tried to be careful, the nails tended to skitter around the room. Collecting (non-rusty) nails in a little bucket is almost as good as an Easter egg hunt to a 7-year-old. Probably.
Picking paint colors: I can spend weeks- months!- picking out paint colors, but the young one has no such hesitation. Zero hesitation, in fact: "green and white stripes!" Hmmm...
Scrubbing: We're not quite to the scrubbing stage in any of the rooms yet, but when we are, we'll totally let him loose with a sponge and a big bucket of soapy water. We grownups might have forgotten how fun it is to play with sudsy, bubbly water, but kids know what's up. And unless a kid accidentally scrubs down a freshly painted wall or something, there's not much that can go wrong.
Hammering nails into scraps of wood: This is a crucial task that no one else will approach with appropriate zeal and thoroughness. If you don't have a 7-year-old available to hammer nails into scraps of wood, don't even bother.
Obviously, all common sense safety precautions apply- and then some, because I'm a worrier. I would love to hear how you have involved your kids in home improvement projects!