Yea ... you would be too chasing a 3 year old and a 4 year old around a lake!!

Plus I hadn't eaten dinner yet ... low blood sugar!!
Umm ... okay ... well, I'm not sure what to tell you ... it could be your posterior tibialis ... strained or the beginnings of tendonitis ... do you do any stretching? There is another post here recently about foot/ankle pain ... I mention a trigger point book in my reply. It should help you too.