What about Singapore? It's hot, but great if you don't want anything too beachy: There are a ton of water parks and splash parks everywhere with toddler areas. Gardens by the bay is incredible for adults and has a dedicated children's garden with water play and a huge park. The evening light show there is also amazing and she would love it- it's not too late- about 8.15, my Dd enjoyed it at 3. Macritchie Reservoir for a bit of a walk and for her to see the hundreds of monkeys! Sentosa- you can go over on cable car which is fun, then visit the aquarium which is world-class. There are also man made beaches if you fancy half a day.
If you want a change, you can go by cheap budget flight to Thailand - Krabi is lovely, had beaches but also a short coach ride away is the emerald pool- natural springs which you would all enjoy a swim in. You can also fly quickly to Bali if you fancy a few days on a beach.
We did California with 2.5 year old DD, and found it a great balance. As Teds77 said, don't be tempted to move too much but you can still fit lots in. There's plenty of beaches, child friendly activities (DD loved a kids science museum that was mainly outdoors), bike riding etc. And the overnight flight back was easy as she slept all the way!
South Africa Cape Town, can see penguins on the beach. We went on a safari too to the big 5 here www.aquilasafari.com, think there's no age restriction on it but check if interested. Table Mountain etc.
Why not a beach? Its just I have done all the holidays listed above and California is fab but not really suitable for a 3.5 year old. South Africa is great but again do watch the age limits for safari. I particularly avoided the ones that allowed kids as they can be difficiult to manage in a open sided truck (my kids were much older).
Mauritius is great. Or Dubai? Disney but at a slow pace. Theme parks day after day are very tiring