The moment when you noticed your child's nails are long...
The moment when you felt that your child is a bit warmer than usual...
The moment when you noticed your lips are dry...
The moment when your child is up for homework...
If you miss these moments, it will be another few weeks until these opportunities are coming back to you, and you would feel bad that you didn't do it then.
That is the reason why I keep them on the top of the wagon.
My list of items from my 'should've' moments.
Sellotape
Thermometer
Nail clippers
Lipsticks
Hole punch
Pencils and rubbers
Every second counts for your family time.