Hi Smurferoos,
U can bring 1 or 2 of her favorite toys onboard the plane to keep her occupied. If u're flying by SQ, u can also ask for the kid's activity pack from the flight attendant(if they do not give out to u). It contains some drawing pads, coloring books & pencils, soft toys..etc to entertain children, so will be handy to keep them occupied for awhile =)
Weather in late Aug will be cooling cos it's springtime, so no worries. Temp ranges bet 18-21 degrees (plus & minus), so just dress in layers & bring along jackets/windbreakers when u're going out in case of chill factor. Springtime is also a gd time to catch the beautiful wild flowers in bloom. And u can see them right at the heart of King's Park
Will u be going to Swan Valley? If so, u can visit Caversham Wildlife Park. It's a great place for kids to get up close & personal with different farm animals & different species of wildlife, like kangaroos, koalas, horses, cows, sheeps.. etc. There, they'll have a chance to feed, hold & cuddle them. Will be a great experience.
U can also go for the The Swan Valley Wagon Trial & join in the different varieties of half/full day tours for an adventure ride onboard horse wagons. Will be a different experience for the family.
Further down from Perth, u can also visit fruit orchards like Raeburn Orchard at Armadale for a free & easy tour on ur own. There, u can get a chance to see the workers harvesting the fruits in season, like apples, pears & pessimons. In addition, they also sell lovely homemade fruit ice creams & sorbets, dried fruits, nuts, preserves, local honey, Margaret River Chocolates, nougat & fruit candy..etc to pamper ur tastebuds. Or if u prefer, u & ur kids can have a go at handpicking some seasonal fruits at The Old Goldfields at Donnybrook if u're planning to travel south. Either one, it's an interesting experience for both adults & children alike.
For some fun out at sea, u can bring ur kid for the Dolphin Watch/Swim Tour at Rockingham (just 35 mins drive from Perth), where they'll get to see & interact with wild bottlenose dolphins. My gal had a great time there. In adittion, u'll also hv a chance get a chance to try some tasty rare black mussels onboard too.
Further down at Busselton, there's also the famous Busselton Jetty which extends 2km out into the Indian Ocean. Walking on, it leads u to an underwater observatory at the end where u get to see different species of marine life deep down in the sea below. If u find walking tiring, just hop onboard the jetty train for a cool & relaxing ride out. Kids will love it too!
Last but not least, there's also a Tumbulgum Farm located at Mundijong, just 40 mins drive from Perth. There's plenty of activities u can do there..like watching & participating in sheep shearing, milking cow, hayride, tasting traditional billy tea, BBQ lunch.. etc. Also an interesting place to be for the whole family.
To find out more abt these places, u can visit their websites at:
1) Caversham Wildlife Park-
www.cavershamwildlife.com.au
2) Swan Valley Wagon Trial -
www.swanvalleywa.com
3) Old GoldFields -
www.oldgoldfields.com.au
4) Raeburn Orchard -
www.visitarmadale.com.au/orchards.php
5) Rockingham Dolphins -
www.dolphins.com.au
6) Busselton Jetty -
www.busseltonjetty.com.au
7) Tumbulgum Farm -
www.tumbulgumfarm.com.au
Lastly, if u need any further info abt other places or attractions, can always visit
www.westernaustralia.com. There's also distance charts & an online interactive map to help u plan out ur routes in advance, so v. useful!
Hope this helps!