By Robin DearingThey keep coming faster and faster, these milestones. Sunday Margaret learned to ride a two-wheeler. And boy, am I exhausted. At first it took both Bill and I holding on and jogging while Margaret tried to gain some control over the pink, Barbie bicycle that Santa brought two Christmas's ago. The girl seemed to be completely lacking in balance. But as we ran and she veered and shimmied, she eventually started gaining some control. Then we learned that it only took one of us to hold the seat and keep her from running to trees and fences — and believe me, it was a good thing, too, because we were getting worn out. So we took turns running up and down the block holding the seat upon which my baby sat. Then she was doing it, she was riding her bike and I was letting go. The instant it happened I started to get that feeling, that one I get whenever Margaret reaches one of those milestones. I immediately got a little misty-eyed and I was excited and just a touch sad. But then she wobbled and rode through the neighbor’s flowerbed and I lurched to grab a hold once again. We laughed together at her crooked riding and she tried again. By dusk, I was running behind her just to make myself feel better. She was doing it all by herself. Monday's holiday began early for us as Margaret was anxious to eat her breakfast and ride her bike. I put on my running shoes ... but I didn't need them. She was quickly leaving me in the dust. By noon she was riding around the block sans parents. As she rode up to me, she said, "I'm so proud of myself. I can ride a two-wheeler all by myself!" I'm proud, too.