All toddlers love familiarity, and many stubbornly cling to a favorite blanket, toy, or food preference. When she turned 2, Jessica Adams discovered a profound love for her pink sippy cup -- as opposed to the green or blue one. "Soon, she wouldn't drink from any other sippy," says her mom Angel, of Altoona, Pennsylvania. "She'd cry and throw a huge fit and not give in until she got her pink sippy." Such behavior gets tiresome for parents, but developmentally it's a good thing, says Maureen O'Brien, PhD, coauthor of Watch Me Grow: I'm One-Two-Three (Harper). "Routine gives kids a frame of reference, a sense of order," she says. "The world is a big, scary place, and if toddlers feel they have control over one thing, it's reassuring to them."
Between 2 1/2 and 5, repetitive behavior often morphs into a single-minded interest in a character, animal, or favorite color. This one-track-mind phase generally peaks between 3 and 4, says O'Brien. "Around 3, their imagination just takes off," she says. "Their thought process is much more complicated than it was at 18 or 24 months." One important new brain development: Kids can see things from another perspective. "Instead of just thinking the ballerina is pretty, a child can imagine that she is the ballerina," says O'Brien, adding that preschoolers dip in and out of reality and "try on" various personas. "Pretending is a tool to express themselves," she says. "Going down the playground slide as Superman might help a child feel in control; roaring like the Hulk helps him release anger in a safe way."
Having a burning interest in a particular character or toy can also help children relate to each other and make friends; they know they have something in common if they're both wearing Tinkerbell outfits or heading straight to the preschool Lego bin every morning -- even if they can't express their feelings in so many words.
Of course, the relentless marketing of every kid-related product, from Transformers to Dora the Explorer to the Disney Princess collection, often gets kids hooked on a certain character or toy. (So many products are plastered with commercial images, it's easy to be cynical and say, "How can my kid not be obsessed?") But just about anything can trigger a burning interest -- a movie, a trip to the zoo, or a character in a book. O'Brien, who has twin boys, says that one of them was into Superman for months. "I finally figured out that it wasn't the cape or the costume," she says. "Rather, he would look in the mirror, take a piece of his hair, and curl it onto his forehead." With the Superhair in place, he felt stronger, and his posture changed. "He was emulating all the good things about Superman," she says.
And not every obsession relates to a TV character. "When my daughter Alexis was 3, she spent an entire month acting and talking like a cat," says Kelly Mooney, of West Linn, Oregon. "She would only 'meow' in response to anything you said, and she wanted to look like a cat -- she frequently wore cat ears." Fortunately, her teachers were willing to overlook her kitty-cat phase for a few weeks, and Alexis gradually began acting like a human being again. (At 7, she still loves cats, but doesn't dress like one.)