An Uphill Goal

The girls love to ride their bikes.  They will ride for miles in the area forest preserves, which always seem to have nice, flat paved paths.  When it comes to riding in the neighborhood, it's an uphill struggle.
They haven't figure out yet that they need to keep peddling, and maybe peddle quicker, when they are going uphill.  This is a problem since we live in a neighborhood with a lot of hills. 
At nearly every hill one of the girls stops peddling.  It could be that the blond twin needs to tell her sister something so important that it cannot wait until she gets to the top of the hill.  It could be that the brunette twin needs to point out a dog in the neighbor's yard.  In any case, one of them stops and we all have to stop to wait for her to catch up.  It's less of a bike ride than a walk and ride cross-training activity. 
I think their inability to make it to the top of any hill is a combination of a few things.  First, they are still small.  It's hard to peddle up the hills.  Second, they just don't seem to realize they need to keep peddling.  They haven't figured out the physics of biking.  Third, they don't see making it to the top of the hill as an accomplishment.  If they do it, they are happy.  If they walk their bikes up the hill, they are just as happy.  
My goal for the summer is to get them to continue peddling up the hill.  It's a small goal that will make our bike rides much more enjoyable.