When the kids started brushing their teeth on their own, I got out a three-minute egg timer and told them to brush their teeth until all the sand ran into the bottom. I wasn’t always in the bathroom watching them, so I’m sure there were many times when they turned the timer over before the sand was halfway through. Below is a photo of the egg timer that they used. I bought it when I was in high school.

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Have mercy upon me, O God,
According to Your lovingkindness;
According to the multitude of Your tender mercies,
Blot out my transgressions.
Wash me thoroughly from my iniquity,
And cleanse me from my sin.
Psalm 15:1-2