It’s possible to reverse shrinking, to a certain extent. The type of garment shrunk matters, as does the degree of shrinkage. The garment is, however, unlikely to recover to its former glory. The simpler the garment, the better the outcome: for example, a scarf or shawl will stretch out better than a glove or jumper. In general, it’s not worth trying this on baby garments: put them on one of the baby’s dolls or teddies instead.
The technique involves wetting the garment thoroughly and stretching it. You’ll need a lot of muscle power to do the stretching – you are, after all, tearing the bonds between the fibres that have snagged together. The garment should be pinned out at its maximum dimensions and be allowed to dry naturally. It’s sometimes possible to repeat this procedure for improved results, but the downside is that the fibres will weaken, and you may tear holes in it.
If this fails, you could gift it to someone whom it will fit! Alternatively, it could be cut up for use as placemats, cushions, or even blankets.