New guying trying this in Southern Maryland

Hello World,
        I'm about to turn 40 and I DON'T want to slow down.  In fact I need to speed up.  My wife and I had twins last fall and I figure at some point I'm going to have to run with them, swim with them and take them for bike rides.    Does anyone here know of a hobby where I can do all three   Truth be told I really enjoy biking and swimming, recreationally.  And I used to be a runner in some younger years.   In one week of training I've really enjoyed the idea of having a new activity to look forward to each day.   I'm doing the 22 week to sprint training plan and it's going pretty well so far.....Except I keep getting this calf pull.  It's very very localized.  Feels about the size of a quarter and only hurts when I run.  Walking, biking, swimming, climbing stairs all good.  Any ideas on how to treat and, more importantly, prevent this from happening?