New York ? The relationship between a parent and a child no matter how close the bond is complicated.

And it doesn’t get easier with age.

Roberta Maisel, a sociologist and mediator specializing in conflict resolution, offers advice on the transition baby boomers and their now-adult children are going through in “All Grown Up: Living Happily Ever After With Your Adult Children” (New Society Publishers).

The key, she says, is developing a friendship. The boundaries of that friendship, however, will vary from family to family and possibly from child to child.

A good starting point, according to Maisel, is to create a new family paradigm, one that’s close to equality but still recognizes the parents’ valuable life experiences.

“Parents have to figure out what they want in their relationship with this other ‘adult,’ while also looking at the needs of your child who will always be your child,” says Maisel, the mother of 43-, 36- and 31-year-olds.

There are ways for parents to relinquish their power gracefully, including parents getting to know the world of their adult children, cultivating their own sense of self and finding new, suitable ways to spend time with their adult children.

Parents also need to learn to hold their tongue. But, that said, parents also need to speak from the heart and be receptive from frank and even critical talk from their children.

“I’m really for parents not giving unsolicited advice or even unsolicited questions, which might seem invasive,” Maisel says.

Reminding a 21-year-old to send a thank-you note for a gift, for instance, isn’t particularly helpful. Sharing raw feelings will put new “friends” on a path toward some worthwhile discoveries.

As for children who want to be treated as adults, they need to be prepared to act as adults all the time. “A young person often wants the freedom to make decisions and do what he wants to do, but then he asks for money,” Maisel observes.

The problem is, she continues, that there are different definitions of “adult.” A child might become an adult when he turns 18 or graduates high school; it could be once he supports himself financially; it could be when he finds himself in a supportive role to his own family.

And many 20-somethings are still in college or graduate school, leaving them and their parents who might be paying the bills in limbo. More than ever, this is a time to set clear parameters, says Maisel.

In her book, Maisel, who lives in Berkeley, Calif., is very candid, saying much of her advice comes from her own life and the challenges she faced with her children.

She interviewed 25 parents in the 48- to 70-range and heard similar tales of hollow telephone calls, tension-filled gatherings or even periods of estrangement.

Somehow, Maisel says, the communication she had with these other adults opened her eyes to see that she could love her children as the “lovely, imperfect, immensely human souls” they have grown to be.