Buying baby food is as simple as picking the cans and containers off the grocery store shelf, but making it at home can be just as quick and easy. If the puree is too thick, you can thin it with breast milk, formula, or boiled water.
Simmer plums, covered, in a large saucepan with 1/4 cup water until tender, about 10 minutes. Transfer plums to a blender. Working in small batches, blend until smooth. Add up to 1/3 cup boiled and cooled water if needed. Pass mixture through a fine sieve for the smoothest texture. Fill 1/4-cup plastic containers or ice-cube trays with puree. Use same method for peaches, apricots, and other stone fruits.