It's the moment every new mother waits for. Your baby looks up at you and smiles—not one of those "maybe it's just gas" smiles but a genuinely joyful smile, as if to say, "Mommy, I love you." A baby can recognize his mother's voice at birth and make out the outline of her facial features at around 2 months. Then, between 3 and 7 months, an infant begins to form solid attachments and show preference for some people over others, usually parents and other caregivers. Renowned child psychiatrist Stanley Greenspan, MD, dubbed this the "falling in love" stage, when a baby can both initiate and reciprocate expressions of love with his favorite people. The love is written all over his face as he smiles, gurgles and laughs to show you affection. "Babies have few ways to show feelings, so their facial expressions reveal a lot," says infant specialist Julia Braungart-Rieker, PhD, a professor of psychology at the University of Notre Dame in Indiana. "And research shows that even when moms work outside the home, their babies form strong emotional ties with them." Want more of those "I love you and only you" smiles? Spend more time playing. Shared playtime will not only elicit loving looks, it will also stimulate your baby's emotional development and reinforce your bond with him, says Dr. Braungart-Rieker. Encourage his engagement with simple games like peek-a-boo and patty-cake. He'll also get a kick out of a gentle foot rub or body massage. To figure out what he likes most, watch for joyful reactions. Then let him take the lead: "Wait for that spark in your baby's face that lets you know he's ready to engage," suggests Dr. Braungart-Rieker.Playful interaction also helps your baby reach motor and cognitive milestones and develop verbal and reasoning skills. As you sing and hum to him, he'll learn to do the same. And as he figures out what makes you happy, he'll develop a routine to make you smile—like grinning, babbling and pumping his arms. His love for you will help him learn to reach for and ultimately crawl to you.Alas, as happens with many love affairs, your baby's initial infatuation will eventually fade. The falling in love phase lasts until 7 or 8 months, about when a baby starts to crawl, Dr. Braungart-Rieker says. He then may opt to discover what's under the dining room table rather than play peek-a-boo, but know that the sense of love and trust you've built will enable him to happily explore his world.    Play It Sweet These easy tips for infant play, from Notre Dame's Julia Braungart-Rieker, PhD, will help keep that loving spark in your baby's eye.