Judy, thanks for your question about your 12-month-old son's sexuality. Babies explore their world with their senses—touching, smelling, tasting, seeing, and hearing—and they begin by exploring their own bodies. Just as it's common for a 3-month-old to enjoy clasping her hands together, a 4-month-old to grab his feet, and a 6-month-old to put her hands in her mouth, it's common for infants and toddlers to touch their genitals.
As you've observed, the most common time for your baby to touch his genitals is during diapering and bath time, when his diaper is removed. The feeling of air or water on his genitals, or a full bladder, is stimulating. It can cause baby boys to get an erection of the penis, and baby girls to get swelling or lubrication of the vulva. The stimulation draws babies' attention to their genitals and makes them want to touch themselves. And as they touch themselves, they experience pleasurable and comforting feelings.
Many parents are shocked and embarrassed when they observe their babies touching their genitals. Think about how your reactions may be affected by your own parents' attitudes toward masturbation and their reactions to you as a child. And think carefully about the messages you want to give your son about his body, his feelings, and his sexuality.
Our current understanding of child development shows that it's normal and healthy for children, beginning at birth, to learn about their bodies and experience pleasurable feelings. You can help your child develop a healthy identity and sexuality by trying to maintain a calm and accepting attitude toward him touching himself, and avoiding any reaction that makes him feel ashamed. Over time, you can help your child understand our society's rules about touching his genitals—that it's natural and private, something he can do in his bedroom or bathroom.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.