I don't think it's fair, and you are right to complain; you pay for class to learn belly dance, not to express sympathy with single mums. Your teacher's attitude makes it sound like your classmate's childcare arrangements are more important to her than your learning bellydance
Maybe she'd rather run a playgroup or a youth club...
IMO she shouldn't have allowed it in the first place - trouble waiting to happen. The minute it upsets other students she should be having a word with mum rather than wimping out like it's not her problem. Pathetic. If none of your classmates will stand up for themselves I don't see what you can do but take your business elsewhere.
As for mum...
she should be hauling him out of there the minute he annoys anyone and sorting it.