Does my child need sailing experience or to be a strong swimmer?

No sailing experience is required for the lower courses. Australian Sailing says no sailing experience is needed to attend them.

The prerequisite listed for Tackers Intro, Tackers 1, Tackers 2, Tackers 3 and Tackers Combined is that the child is "water confident" and aged 7 to 12. Little Tackers only lists the age (4 to 6). The course pages do not define "water confident" or set a swimming test.

From Tackers 2 up, children also need the skills, knowledge and experience from the previous level: Tackers 1 before Tackers 2, and Tackers 2 before Tackers 3.

Source: https://www.sailing.org.au/news/tackers-program-kids-boats-fun and the course pages at https://www.sailing.org.au/courses