The youtube videos of mother fox feeding her babies uploaded by Luc Durocher and Balkan Music on 2014 and 2016 respectively, refutes the claim.
Few of the social media users shared the video claiming that Fox feeding milk to her babies who lost their mother in Australia bushfires.
In 2014, YouTuber Luc Durocher uploaded the video, which shows a red fox is breastfeeding her kids with the caption "Red Foxes - Feeding." The other YouTube channel, Balkan Music also uploaded the same video in 2016 with the caption Mother Fox feeding her babies.
Hence, it is confirmed that this video is of 2014 and it is not related to the Australian bushfires 2020, and also the mother fox is feeding baby foxes but not koalas.