Time Flies When You're Having Fun

Not that I'm looking for an answer to this, b/c I really don't think there is an explanation for this phenomenon...but WHY does it seem to take FOREVER to get past the baby stage when you're so sleep deprived, can't figure out why they are crying, and going out w/ the baby feels like you're packing for a week long trip, but time FLIES when you're at the fun stages? For me anyway, it seemed like it took forever to get to the 3 or 4 month old stage when they aren't so colicky, and are finally on somewhat of a schedule. But then once we got there, and to other big milestones, now it just seems like time is on fast forward, and I don't like it!
Here are just a few things I can think of that the boys say or do lately that is just not baby-like anymore.
Levi used to close his eyes very calm, and serene-looking when we prayed, now he squints them shut trying to peek out and look.
Wyatt asks me to "drop him off" when we go to someone's house for a play date. One time he even asked me to drop him off at the store, so he could stay ther by himself! ha!
Levi says "Mom" instead of Mommy most of the time ("Thanks, Mom". "I can do it, Mom")
Those are just a few.
But I enjoy some of the things they say and do that are still baby-like:
They both say "Forsie" (for Horse). Wyatt says "Grills" (for Girls)
and of course I love, "Mommy Hold Me"
One area I wouldn't mind if they "grew up" in, is potty training, and just the whole start-to-finish act of going to the bathroom!
Here's a pic of my "big" boys!