Visiting UK in Dec--need advice on traveling with children and siteseeing

Hi there.  I love this board and wish I had known about it when I lived in London in '99/'00. 

My husband, 3 yr old and I are visiting London for a few days in December (27th-30th) on our way back from X-mas in Portugal.  I am so excited.  I miss London so much and am always begging my husband to consider moving back because I think our son would so many more opportunities. 

ANYWAY........We are staying at the Marriott in Maida Vale, and I am wondering if we should rent a small stoller?  My initial thought is it would be too much of a hassel with Pub transport.  But I am concerened that my son may get tired of walking.  During our few days in London we are hoping to visit the Aquarium, and the Eye.  Plus we will probably visit our old stomping ground -East Finchley and a few places in the Earl's Court area. 

Should I go with my gut instinct?  or should I rent a small stoller (hopefully one that is foldable) or should I bring an umbrella stoller with me?

2 other questions.......
1.  Can anyone give me their opinion on the aquarium?  Is it worth our time? 
2.  What about indoor play areas for kids (i.e.tunnels, jummpy things, ball pits) can anyone suggest some in the London area?

ANY suggestions on things to do and stollers is greatly appreciated.
Thanks
Melissa 

you can probably buy a cheap as chips pushchair from Argos which will cost you less than renting one (I bought one for £9-12)  I when I traveled with our daughter I just got a sling it worked for her till she was 5 years

http://www.cuddlekarrier.com/WEBFRONTPAGESM.jpg


some people told me that the Aquarium was good because they have a petting area but in my opinion I felt she was too young and was not into thing behind glass but all children are different.

There's also the city farms to look for. My recommendation is to get the Time out "London for kids" guide. If you are going to go to East Finchley than you're not far from the New Arts depot in North finchley they will be showing "the little mermaid" which will be puppetry I think

http://www.artsdepot.co.uk/mermaid.php

anyway hope that was helpful

Ahttp://www.familiesonline.co.uk/article/static/1087/ 
 

 
as far as indoor play goes, this might help...we do the wacky warehouse near us all the time.

Thank you for your suggestions........I really appreciate it!
Melissa