On a more serious note, it might just be a phrase used in the idea of, you should have a kid...like a command.
What should I do now grandma...I'm 30 years old...have money a nice wife etc but I feel unfulfilled.
Avoir un enfant. (although avoir would probably be used in the imperative actually).
Nonetheless, context isn't alway the point in Duolingo. You can still learn the english phrase, 'to have joy'. 'to have a dog'. Then combine it later with what you know.
- J'aimerais avoir un enfant.
Walking along a busy market somewhere in Asia and you approach a rather noisy stall out of curiosity which turns out to have babies on display and before you know the seller jumps in your face, forces one of the babies in your hands and goes: "Have a child!".