Social bonds and supportive relationships are widely recognized as being indispensable to healthy psychological functioning and well-being. Using the 2001-2016 Household Income and Labour Dynamics in Australia (HILDA) data and a multilevel approach, we assess the impact of parental social support on the individual’s capacity to establish adequate social support in the future. Our sample includes 1,109 Australian young adults aged 21-28 (among them are 609 siblings). The level of social support as perceived by their parents is measured during childhood/adolescence. Our findings show that, in addition to individual characteristics and other parental outcomes, parental social support is an important predictor of the level of social support experienced by young adults. Focusing on siblings, we confirm this evidence, finding that some individuals experience more social support in their twenties than other individuals as a result of the family environment in childhood. In particular, parental social support explains about 16% of the initial sibling variance. Finally, we find that parental social support is also positively associated with the level of trust and networks experienced by young adults. Thus, both trust and networks seem to act as mediators for social support. That is, to receive social support, an individual needs a network of people linked to her/him and she/he needs to have trust in others to accept support.