April is gorgeous here. Still lots of sunny T-shirt days but none of that stupid hot weather. I love Fremantle so I'd say it is a great place to stay - for kids and the grown-ups. Or you could try somewhere more central and cosmopolitan like Subiaco or Mount Lawley - both have lots of shopping and restaurants and easy to access kid-friendly places. Depends what you like.

The hills are also beautiful - Kalamunda markets, Mundaring Weir (I love the pub there, and lots of families have Sunday lunches there so little one friendly), Rollystone National Park etc.

For the kids there is lots - the beach, the zoo, AquWA, Kings Park, just lots of outdoor places. Depending on how long you are here I'd also recommend a trip down south.