Probably already on your itinerary but the kids/toy section of CBD Myer is worth a visit. So is Minotaur on Elizabeth street even if both are a bit lean on TF's at the moment.

If you're here on a Sunday, check out the Diamond Valley Railway in Eltham. Kids will get a kick out of the miniature railways they can ride on and it's an impressive spectacle for adult riders too.

Otherwise Funfields in Whittlesea or the Carribean Gardens Market in Scoresby are very kid friendly. But they're a fair bit away from the city centre and you'd probably have to commit a day for each of them.