"I am here with a mom."
Translation:Я тут з мамою.
I don't have a problem with the Ukrainian. But nobody would say in English, "I'm here with a mom." Duolingo is trying to directly translate Я тут з мамою. by adding the article "a". There is no direct translation into English, only approximate translations. It wouldn't be incorrect just to leave out the article, except that it becomes a proper noun, "Mom." Other than that, the Ukrainian implies that мама is моя. That's why in English it should be "my mom," explicit not implied.