A teenager is barely an adult. There will be times when the child surfaces above the parent status. And keeping things in the balance can be extremely hard without proper moral support. If they are secure financially, I'm afraid their biggest challenge is when the teenager's child became a teenage, the parent might unconsciously return to the teenage mode to salvage the years they had never fully experienced as carefree as it is natural, especially for teenage parent that has just past puberty; a higher percentage of them has suppress yearning to live out the phase.
By stating my opinion and mine alone; does NOT mean that teenage parents are not loving, caring and responsible. This is an answer to the question: What are the biggest challenges of teenage father/mother? That also suggests 'one' parent only, and a little more harder emotionally and mentally.