Introduce your baby to lentils when they are 6-9 months of age. Closely related to the pea family, lentils are a great source of protein, calcium, iron, and carbohydrates. You may worry about the gassiness of lentils, but if given in small quantities it should be fine. To make digesting them easier, soak them, remove the water, and then cook them. Another suggestion is to cook the lentils very slowly (1-4 hours depending on the type) such as in a stew or soup.
Red lentils - 15 minutes
Green lentils - 20 minutes
Brown lentils - 35 minutes
Lentils can be mixed with other vegetables (e.g. carrots, broccoli, squash, etc.) to make a delicious puree.