Is My Baby Smiling, or Does She Just Have Gas?

"Between four and six months of age, the baby is smiling, giggling, and very fun to have around," Dr. Jacobson says. And around five months you might be able to elicit a full belly laugh. But it's not uncommon if babies start laughing sooner or later than that.

And fair warning, it's not all giggles for everyone: "By six months of age, the baby also has good grasp, so they pull hair very well," Dr. Jacobson warns. Watch out!