Thanks for pointing me to the right direction.
After some more search for free apps and and a quick run through to see how intrusive ads are, i found that animal sound box and sound explorer: animals are reasonable and with less intrusive ads.
However, i did not find anyway to remove ads from these (or may be there is). Other one or two apps that i quickly went through had full page ads (gosh these are apps for kids for crying out loud. Find another way to make people click ads).
Sarshah.