These 4 must-know tips will help your family mesh no matter what your circumstances.

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You already have one or more children of your own, but you feel you have more to give. Or you tried and tried to get pregnant but couldn't -- then adopted and promptly conceived a healthy baby. Whatever the circumstances, your brood consists of an adopted child (or more than one) as well as one or more biological kids. Here's what can you do to ensure a harmonious and happy family life when you are not the birth mother of all your children.

How to prepare existing kids for a new arrival

Whether your biological kid is getting an adoptive sibling or the other way around, you need to prepare the child for an addition to the family. "Talk to your child about how you want to grow your family: 'I had siblings, and I want you to have them too,'" says Rita Taddonio, a licensed social worker and head clinician at Spence-Chapin, a private, not-for-profit adoption agency in New York. "Kids think everything is about them. You're making it clear that this is not about your child, so he doesn't think, 'I'm not enough.'"

Involve your kid in the preparations by getting him to help decorate the new baby's room or pick out toys. If you're adopting, let your kid attend a family meeting with the social worker and ask any questions he has. Give older kids a role, such as changing diapers or reading books to the new sibling. And make it clear to your child that he'll still have one-on-one time with you -- then plan for it, even if it's only an hour a week in the beginning, Taddonio says.

If you adopted after struggling with infertility and now are expecting a baby, it's important to really drive home that your adopted child is a permanent member of the family who could never be replaced. "Really affirm that your love is rock-solid, no matter what," says Bobbi J. Miller, Ph.D., a licensed family therapist who specializes in adoption and an assistant professor of family and community medicine at Saint Louis University. "Adopted kids might say things like, 'I wish I had grown in your tummy.' You have to be okay with that grief and tell them you completely understand."

The Child Welfare Information Gateway, the National Resource Center for Permanency and Family Connections, and the Minnesota Adoption Resource Network offer guidance on sibling relationships in blended families.

How different is the blended-family dynamic?

In terms of interaction between the kids, adoption doesn't tend to have a huge impact, Taddonio says: "We see typical sibling rivalry, as in, 'Mom loves you best because you're adopted; no, she loves you best because you're her biological kid.' Adoption is just the word they stick in there."

One land mine to watch out for is going overboard with special treatment for the adopted child, which can have negative effects on both adopted and biological kids. "Parents become so worried about the adopted child's not feeling wanted, but the idea that adoption makes him the 'special child' tends to give him less room to say, 'Sometimes I don't think it's a wonderful thing that I'm adopted,'" Miller explains. "Also, other kids in family might say, 'Wait a minute, am I not so special?'" Taddonio adds that it's not healthy to exempt adopted kids from tasks all kids hate, like household chores. Treating them differently can make them feel like a guest in the family. The Child Welfare Information Gateway offers information on emotional issues that can crop up in people who were adopted, and how to help them through these.

"My kids get along like brother and sister -- they fight, cuddle, play iPad games -- it's a joy to see," says Tricia Corcoran, 49, of Kings Park, New York, who adopted her daughter at age 1 when her biological son was 6. "In the end, it's been everything that I wanted."

Does your family need help?

A certain amount of sibling rivalry is nothing to worry about, but if one of your kids is displaying personality changes, behavior problems such as strong temper tantrums, or regression such as bedwetting, or if your kids are asking you questions you're not sure how to answer, then your family might benefit from professional help. Stay in touch with your adoption agency, and take advantage of any support groups or counseling services it offers. The agency can refer you to a therapist or psychologist who will meet with your whole family and determine who needs what treatment.

"Don't be afraid to interview a prospective therapist about her experience with adoption," Miller says. "Experience is important, and not everyone has it." The Child Welfare Information Gateway and the American Association for Marriage and Family Therapy offer information on finding the right professional for you.

Copyright © 2013 Meredith Corporation.