Nina quit working as she neared the end of her pregnancy and stayed home until Isabel was 14 months old. Then she hired a housekeeper and returned to her job, but was free by midafternoon.

Nina couldn't wait to get home each day to see Isabel. The joy and security of their relationship was evident through their happy reunions.Nevertheless, Nina felt that a distance was growing between them. "She loses interest in me so quickly," Nina said. "It's a funny thing, because I know nothing is wrong."

The mystery behind the "distancing" had nothing to do with Nina. It had to do with play. Isabel had moved into the toddler stage when her mother went to work, and now her joys came from play at least as much as they came from closeness.

While Nina found it easy to cuddle Isabel, she had a harder time playing.

"I find something that I think would be enjoyable for Isabel, and I try to do it with her," Nina said. "But it never holds her interest for very long, and frankly, I get tired of trying to entertain her and hold her interest."

The relationship between Nina and Isabel changed when Nina stopped trying so hard to plan the play. She allowed herself the time and flexibility to slip into play that was already going on. She learned that Isabel's play was really her major job.

Playing with a toddler requires very real shifts on the part of an adult. Mother or father must be willing to sit on the floor because that's where the toddler is most comfortable. They must also be ready to make quick shifts in response to the toddler's short attention span.

Playing with a toddler also requires a shift from language and thought to noise and feeling. Toddlers move back and forth between using sounds as part of make believe and experimenting with sounds to form words. Naming and learning with the parent mostly comes after the parent is willing to share in the noises and just plain fun.

Some parents try to play with their toddlers without really paying attention. They may be thinking of what they have to do next, or talking with their spouse or other children. But the point of playing with the toddler is the joy that comes from it.

When parents actually enjoy the play, they are giving an early message that relaxation, flexibility, and happiness are most important. This becomes part of the child and provides a major building block for a healthy personality later on.

People who do not have the opportunity to grow up with play as their central activity generally have a different baseline - tension, work worry and getting something accomplished.

Play with a parent also allows the youngster to experiment in an easy way with different phases of growing up.

For example, Isabel is now 19 months old and is beginning to experiment with being her own person by acting oppositional.

She and her mom play building blocks and taking turns. Sometimes Isabel doesn't let her mom play with the blocks for a minute or so. Other times, she knocks down her mom's tower - only to ask her to build it again. It is no coincidence that Isabel is not very negative when she is not playing, limiting her opposition to an area that doesn't create tension in the family.

Play with toddlers also is important for fathers. As babies move out of infancy, they are more interested in their fathers, just at the time that play becomes their most important work. Fathers make friends of their toddlers by getting on the floor with them.

It seems common sense to say that playing is important for toddlers and preschoolers. But it is another matter for adults to shift away from a busy workday to a youngster's world. Parents must be willing to sit and watch and listen, until they get the hang of it.

There is a large gap between an adult's grim determination to be in full command of life, and a child's total, imaginative playfulness. When the shift can be made, a toddler has a parent who is also a friend.

*Dr. Schwarzbeck is a consultant to families, schools and hospitals in the Seattle area.