I`m trying to make a good plan for our 3,5 day in Singapore. We are travelling with 2 small kids (4 and 5 years old). Look at our schedule please and give some advice, because I`m lost in so many web pages about Singapore

3 Dec 11.30 am we`re landing, our hotel is V-Bencoolen.
7 Dec 6 pm we are leaving Singapure
We would like to see:
1. Aquarium (or Underwater World and Dolphins Lagoone, which is better for kids, who love fish and reefs?)
2. ZOO (is there special attractions during weekend?)
3. Jurong Bird Park
4. River Safari
5. Legoland (is there special attractions during weekend?) How to get there in low cost?
6. Garden By the Bay
7. The Botanical Garden
Is it realistic to see it all during this time?
Where can I buy the cheapest city passes?
Is it cheaper to take public transport for our family or the taxi?
Is there any problem with finding a tourist information in the city? Connecting with wireless will be very expensive for us.
I`m searching at groupon.sg and deal.com.sg is also, it safe and easy to buy tickets there? Should I print my ticket from e-mail or is it necessary to pick up the ticket from specific place in Singapore?
I will be so gratefull for answering my doubts.
Best regards
Monika
Poland