Pregnant women typically have an expanding belly and large breasts. You may want to look pregnant even if you are not pregnant for a wide variety of reasons. A girl might be portraying a pregnant woman in a play or she might want to learn what pregnancy feels like in order to empathize with a close relative. She may also want to prepare herself for her own pregnancy one day. Making a girl who is not pregnant look pregnant is not a difficult task.
Wear a larger sized bra. Most pregnant women who are in the later stages of their pregnancies have much larger than normal breasts. Fill the cups of the bra with soft, small pads such as washcloths. Aim for a natural look that does not have wrinkles. You can purchase inserts to place in the girl's bra that are typically used for nursing women to help them stop leaks. There are also rubber inserts that can be used to expand a woman's cup size.
Purchase spongy materials from a craft store. Foam also works well. You can also use a pillow insert commonly used by crafters as a base for a pillow. Look for sizes that are large enough to fit around your waist comfortably. Bring a measuring tape with you when you go to the store. Aim for material that juts out about three to six inches from your waist for the most realistic effect.
Sew two pieces of elastic to the ends of the foam or spongy materials. Fit the material around the girl's abdomen. Center it around her belly button. The material should have an even, round appearance and flatten out towards the ends of her stomach. It should reach to the top of her hips. Pull one piece of elastic to fit under her breasts. The other should be pulled around her hips. The fit should be snug but not too tight. You should be able slip one finger between the elastic and her flesh.
Wear a maternity dress. Any maternity dress should be loose enough to allow someone to see that the girl is pregnant. Do not make it too tight or the effect will look weird and fake. A good size should reach at least her knees.
Have the girl carry objects associated with pregnancy such as books about having a baby or baby accessories such as stroller, baby bottles and diapers.