If warmly supportive parents are especially likely to have children with high self-esteem, this would most clearly indicate that

This would most clearly indicate that: Warmly supportive parenting and children's self-esteem are correlated.
Warmly supportive parenting tends to give enough encouragement for the children to follow their desire and support them in their decisions.
This characteristic would make the children much more likely to grow up with a higher self-esteem.