Is there any way to unlock baby daisy, bowser jr., and dry bowser besides getting a star on certain courses?

Any help?

Baby Daisy - Play 1,950 races
Bowser Jr - Play 3,450 races
Dry Bowser - Play 4,350 races

It may take some time (months if not a year) to get 4,350. I think that any time trial, VS, GP, etc counts as a race. The quickest would be to do a load of 32-race VS mode matches, that means, 61 of these in total to get 1,950 races, 108 for 3,450 and 136 for 4,350 races. So, if you, for example, did 5 per day, well, it'd only take you a maximum of 27-28 days.... and that's if you started from nothing. Assuming you've already played this for some time, you've probably gotten a number of matches. You can see how many races you've had by going to License Options (located on the main menu screen, where you have "Single Player", "Multiplayer", "Nintendo WFC", and "Mario Kart Channel", in the top right corner, and selecting Records. It's listed as "Total Race Count".