Do you have a patch of yard that can be turned into a garden? Or a place to grow plants or vegetables in pots? Bring your kids to a garden store and offer to buy a few plants if they can read the name of the plant and the directions for care.
After planting them, give your kids a small notepad they can use to follow each one's development. Ask your kids to write full (but simple) sentences that are punctuated and have correct capitalization. You can use this opportunity to talk about proper and common nouns. You can also give advice about using adjectives to describe the growth your kids see over time.
Extend this activity by taking photos every few days with a digital camera or your smartphone. Show your kids how to email and print your pictures at home, or take them to a local CVS and use a printer kiosk. Prints are only about 20 cents each!