For basketball you might also want to look at Eltham Wildcats. It's only a 10 minute drive from Doncaster but they have lots more teams than Doncaster, great for beginners. My kids play Saturdays, whether its Doncaster, Bulleen or Eltham it's all the same competition (EDJBA)
The best sporting clubs in Doncaster for children are Doncaster Basketball Club (Leeds Street) or Doncaster Football Club. Both these clubs are very professional and well disciplined and children will learn heaps at these clubs. Friday night and Saturday night basketball is available at all age groups and football is played on Sunday's.