H.B.
I know you said you would rather have a night class but I have taken Abrea's step class and it is far from beginners. She is the head of the dept and will get you into great shape. She has a Tues and Wed 9:45 class so its not too early to get there with a young child. You could always do a day membership for free (guest pass to try the gym) take the class and make sure you like it before you go to all the trouble of switching.
Good luck
H.