Children's furniture, those smallscale pieces that are often miniature versions of full-scale adult furniture, cost just about as much per pound or square inch as their grown-up counter-parts.

Cribs have limited use -- it's downright impossible to stretch one to fit a growing child. Child-size bureaus scaled to fit by tiny garments are not very practical for the blue jeans and bulky gear of the sweater set.

But at last, manufacturers of children's furniture are beginning to get the message. Infants' furniture that is convertible for older children -- even adults -- is now being made.

In a new line of furniture on the market, the crib is ingeniously concocted of three pieces. One is a bureau; the second piece is a platform the width and length of an adult bed, with deep drawers beneath; the third piece is a conventional crib-like frame.

For a tiny baby's room, I used one of these smart set-ups in a delightful wicker finish. Everything I used in the room was meant to be convertible.

Storage shelves fixed to the wall would some day hold books and records. For now they were a perfect place for stuffed animal toys. A bentwood rocker, a comfy place for baby's feedings, could later become a teenager's treasure.

And, you guessed it -- you can adapt this ingenious idea yourself. The standard twin-size platform is available at any loft-bed store. Buy it with or without drawers, or with an additional pullout bed for overnight guests.

The chest is your basic unpainted variety, placed on one end of the platform and facing out so its narrow sides form the ends of the crib arrangement. Choose a size that fits the width of the platform. Wood screws through the bottom of the chest can be fastened firmly to the platform. The crib later can be disassembled easily with a screwdriver.

To make the sides of the crib, attach two 4-foot lengths of 1-by-1 inch lumber to the wall where the crib will stand, and another pair to the back of the chest. To these, fasten accordion-type gates, available at any hardware store, to keep children from falling. One on each side, pulled out and fastened to the opposite strip, forms the sides of the "crib." They are easy for you to open but tough for baby.

A standard crib mattress is all you need to be ready for baby -- and for baby's future needs.