I'm a new father and a mountain biker, I think owe it to your kid to keep on doing the things you love. You will obviously have a different schedule, but maintaining things in your life that make you happy eg. biking will make you happy, therefore a better partner and father. If possible see if you can make cycling into a part of your day eg.if you can bike commute (no substitute for mountain biking) it will keep you in shape for when you get to go riding