When you're out and about at the park or the grocery store, start pointing out babies to your child. Remind him that the big event is around the corner by saying, "We're going to have one of those soon." Encourage him to talk about what he expects life will be like once he becomes a big brother.
Like other expectant moms, your body relies on your iron stores to support the placenta, only even more so since you're nourishing more than one baby. Incorporate lots of iron-rich foods like lentils, chickpeas, and leafy green vegetables in your diet, and ask your doctor about taking a supplement.