It is possible to unshrink wool that someone (not you, of course) popped into the dryer and is now small enough for little Bruiser to wear.
And pretty much all you'll need to do is help your sweater fibers relax, too, with a little help from baby shampoo worked gently into the fibers while washing it by hand.
The most time consuming part: Pinning, stretching and pinning again, to gently unshrink wool to return your sweater to its original size as it dries.
To unshrink wool, start by soaking the sweater in a sink or bucket full of warm water and about two tablespoons baby shampoo. About 15 minutes should allow enough time for the shampoo to relax the fibers enough so that you may begin the letting-out process.
Remove the sweater from the soapy water, then rinse in cool water to remove all shampoo from the fabric.
Gently press or squeeze remaining moisture from the fabric. Don't wring - this can further damage and even break the fibers you're trying to stretch.
Follow your rinse and squeezing routine by rolling of the sweater in a clean, dry towel. It's important the fibers contain as little moisture as possible when you begin the resizing process.
Pin the sweater to a cork board, stretching the neck, arms, and sides as taut as possible without damaging the fibers. Let it be for at least an hour.
Return to re-stretch and re-pin your sweater every few hours. It will take several stretching and re-pinning sessions to ease the sweater back to its original size. But if you adore that angora, cotton, silk, cashmere or wool sweater, you'll be delighted with the results.