there's Magic sing. It looks like a simple dvd player and mike and has tons of music. However, the players that you saw with all those speakers etc. may be the ones with better sound. I have heard that there are other brands out with these speakers and these have better sound quality than the simple magic sing. It makes your voice sound more professional.Go to Sharaf to ask about this and I have heard to the karama electronic shops. I dont know the exact specifics though.
kidzania is good. check the website for an in depth info. its like a small city where the kdis have lots of stuff to do i.e. role play etc. they can stay for hours inside on end.. after that, take them to the skating rink in dubai mall as well. then at night, have dinner by the dancing fountain.