The trouble with kids' clothes is that kids continually grow out of them. About two months after you shell out $100 for clothes at Old Navy, they'll be tight at the seams. Then they'll be relegated to the bottom drawer, and from there it's on to a younger sibling, a garage sale or the thrift store. Smart parents just skip the retail level and head straight for the secondary market -- the garage sales and thrift stores -- where little-used, name-brand kids' clothes are cheap and plentiful. There was much rejoicing among thrift-store aficionados last fall when the Salvation Army opened its Super Store on Broward Boulevard just east of I-95. Clean, well-organized and brightly lit, the Super Store is Saks Fifth Avenue for the tightwad set. There is an excellent selection of boys' and girls' duds, and you'd be hard-pressed to pay more than $3 for any single item (though shoes might run you $4-$5). You're guaranteed to walk out with a bag full of clothes for less than $20. And remember -- you're under no obligation to tell anyone where you got the stuff.