A new study conducted on middle-aged parents giving a helping hand to grown up children has shown the tendency of parents to play favourites even at that stage in life.
The research, carried out by the Purdue University, found that parents are happier helping children who are more successful and settled in life.
Karen Fingerman, the Berner-Hanley Professor in Gerontology, Developmental and Family Studies, revealed that not all grown children get the same support.
Most people expect parents to help their youngest child or one that is struggling, but the family studies expert found that parents are more eager to help the child they consider most successful.
Parents are motivated to help their successful young-adult children because their achievements are a reflection on the parent.
After 18 years, a parent has put a lot of time and energy into raising a child.
When the child is successful, the parent feels like all that effort paid off, and the parent feels successful, too, in their role as a parent.
"Another possibility is that these middle-aged parents expect the successful child will help them during old age," she said.
"I don't think people are deliberately that strategic, but it is a reality that the adult-children who are better achieving will help their elderly parents more.It's certainly a good investment for the parents, but it's also a good investment to rescue your children who are having problems.
"While parents may want to spend more time with the successful child, they may be more likely to give financial assistance and practical support to a child who is having problems.
"We found that middle-aged parents help each of their grown children with many types of support at least every few weeks.
"This is a dramatic increase from 20 years ago, when young adults received much less support from their parents," she added.
Fingerman and her team evaluated how more than 600 parents, ages 40-60, reported they supported their individual children and for what reasons.
The forms of support included financial, helping with tasks, giving advice, emotional support, listening and participating in social activities.
The study will be published in this month's Journal of Marriage and Family.