I've just taken a quick look at the official tourism site for Krakow. The most exciting thing for young Ollie would probably be the Aquapark. (Check out the links, down the left of the page, for more information about the city):
http://www.krakow.pl/en/turystyka/aquapark.php
For spectator sports, Krakow has two professional football teams. Wisla Krakow is one of the most succesful teams in Poland. Their fixture list is probably somewhere on their website:
http://www.wisla.krakow.pl
Cracovia also play in the top division. However, for real excitement, see if you can fit in an ice hockey match. The local team are Comarch Cracovia:
http://www.cracow-life.com/krakow/where_to_pla y/entertainment_details/728-Cracovia_Ice_Hocke y
(There's a link to the club website from that page. If you hunt far enough you should find the fixture list but, because the site is in Polish, it might take some time! Alternatively, I'm sure that an e-mail to the club will get you the required information. NB: The website is actually for Cracovia FC. You have to click on the relevant tab for the ice-hockey team).
You want a zoo? No problem:
http://www.cracow-life.com/krakow/where_to_pla y/entertainment_details/66-Krakow_Zoo
Ollie might also enjoy the Oceanarium:
http://www.cracow-life.com/krakow/where_to_pla y/entertainment_details/675-Oceanarium
Chris