"My birthday is in November."
Translation:Il mio compleanno è in novembre.
I wish I had seen this comment earlier. It just couldn't understand what was going on with those articles. Eventually I found the rule you mentioned in another site (oneworlditaliano btw, it has helped me with grammar). It also said that when the possessive is 'loro' you always put the article -even in singular. So it is: il loro figlio - their son, i loro fratelli - their brothers. I think Duolingo should put a note clearing that out. It would save a lot of time.