Long-tailed Finches (Poephila acuticauda) breeding in natural cavities and nest-boxes were monitored during the breeding season, between March and September 2008, as part of an ongoing field study near Wyndham, northern Western Australia. Towards the end of the breeding season, two adults and their son, who had fledged 4 months earlier, were observed together over many days feeding nestlings (10–17 days old) produced by the adults in another breeding attempt. This is the first description of cooperative breeding in an Australian estrildid finch. Based on these observations, we do not intend to suggest that the Long-tailed Finch should be considered a cooperatively breeding species, but such data help us to understand the variation that exists with respect to familial relations and parental care and provides a foundation for work addressed at understanding the evolutionary origins of cooperative behaviour in birds.