Chances are your preschooler made you an adorable Valentine at school or day care and proudly thrust it into your hand as he planted a big kiss on your cheek. So don't be surprised if someday soon he grabs you and intently asks, "Mommy, will you marry me?"—if he hasn't already. He might even scold your husband, "Don't kiss Mommy. She's my wife!" No need for guilt, Mom. His sudden possessiveness is not because you work and he's desperate to see you more.Your child's intense attachment is one of those relatively common developmental stages, according to Susan D. Witt, PhD, a professor of child development in the family and consumer sciences department at the University of Akron. "Preschoolers are affectionate to begin with," she says. "Then their world becomes bigger and they have many more experiences. So your child notices and processes things like affection between you and your spouse." Since there's a good chance he already identifies with Daddy, he may now think, I'm going to marry Mommy when I grow up. This behavior, which might last up to a year or so, can happen with a single parent, too.

Meanwhile, your son might help out more in the kitchen to be close to you, says Dr. Witt. A preschool-age daughter may watch her dad shave or seek extra cuddle time on the couch with him. Plus, resentment of the same-sex parent might simultaneously occur: Your daughter may push you away so she can hug Daddy. Your son may say to his dad, "No! I want to hold Mommy's hand, not you."

Not to worry, says Dr. Witt. This is something that just happens, so don't make too much of it. If your enamored son shows resentment toward his father, you could say, "Mommy can have only one husband, so you can't marry Mommy, but you'll meet someone that you'll love when you grow up." If a child becomes extremely resentful of the same-sex parent, both parents need to examine whether they're encouraging the behavior in some way—unconsciously or otherwise—and adjust their own actions to temper it.

This stage will ultimately pass as your child develops cognitively and understands he can't marry Mommy but can grow up to marry someone like her. Remember that pretty soon the harder stuff will come, so have a sense of humor about this show of affection. It can simply be fun to hear your daughter say she wants to marry Daddy or your son declare his love for you. It shows your child is a loving person who can feel closeness—even if you're his one-and-only Valentine for only a little while.

Cool cross-gender activities To bust gender stereotypes and show Mom and Dad in another light: Play with action figures, do yard work or wash the car with your son—and get your clothes dirty, Mom. Dad can bake a cake or go clothes shopping with his daughter. Dad should be sure to give her compliments, too. Mom, take your son (and/or Dad, take your daughter) to work to show your child that you have varying life roles—and to enjoy some one-on-one time as well.