Sometimes I wonder whether having children brings greater helpings of joy or sadness.

On the one hand, my two kids are responsible for some of the greatest highs I’ll ever know. Seeing my daughter for the first time, looking up toward me with enormous blue eyes. Seeing my son for the first time, his high-pitched cry filling the delivery room. My daughter and her princess dresses. My son and his fireman duds. My daughter in her first play. My son taking his first T-ball at-bat. I love being a father more than anything I’ve loved before, and I would—without a moment of hesitation—surrender my life for theirs.

And yet …

Being a parent can be so sad. And hurtful. Pre-kids, I paid very little attention to the passing of time. I went about my life happily, naively, bagel by bagel, movie by movie, kiss by kiss. It’s not that I didn’t see myself getting older—certainly, I did. But, save for the annual birthday, there wasn’t a true marker of the days. I lived one day. Then another. Then another.

With children, however, you can’t help but become painfully aware. For example, earlier this week we took a two-day trip to Disney World—our first visit to the park in five years. The last time we were there, my son was 3-months old and, obviously, unaware of anything. My daughter was 3 1/2, and in her element. She wore her princess dresses. She gleefully danced with the characters during the buffet breakfast. She was on a cloud, as happy and innocent as one could be.

Well, this time—at age 8 1/2—she just wasn’t the same. The dresses are long gone, donated to a neighbor. The dancing—over. We went to that same breakfast, and she watched from an icy distance. Disney World remained wonderful and fantastic and joyful. But, well, just a wee-bit less magical.

Which hurt me to the core.