Children can be really mean, even if they don't really understand what they're doing. Kangee probably went to the party, heard Irie say something like she hates Kangee, breaking the baby's heart.
It's definitely Irie's mom's fault for not seeing the way Irie doesn't like to interact with Kangee. Irie's mom should have taught her to be kinder to kids younger than her, not say things she doesn't mean, and Irie's mom definitely shouldn't say they would be married in the future.