Well I suppose their first concern would be the stability of the parents' relationship, if there is one. You didn't mention this so not sure? If you plan to keep the little one, then I would say, just show them that you have thought through how you are going to take care of the baby, & don't cry when you tell them! You may be young but once you have decided whether to go through with it, focus on the positives & embrace the fact that you will be a younger mum!
And if you decided that abortion is an option you'd consider, remember that the most important thing is your happiness.
Whatever you choose should be the right choice for you, not other people!