Explain the expression "the days are long, and the years are short" as it relates to raising children.
Every day you're exhausted and pushed to the limits.  This can be from lack of sleep, because your child is waking up every few hours.  Or it can be because whatever it is you're asking of your child,  they don't want to do it.  Or it can be because the strain is affecting your own ability to be kind and loving to both yourself, your spouse, and your children.  Whatever the reasons,  the feeling at the end of every night is one of utter exhaustion, where presumably this feeling is now your life, and will be so forever.  But, in that exhaustion, it can be hard to either notice or truly appreciate beautiful little moments simultaneously occurring. For example, you might not pause to appreciate when they laugh at something you say or funny face you make.  Or maybe you miss the beauty in witnessing their frustration and struggle as they persistently try to fit that round peg in the square hole.  Or maybe the way they mispronounce certain words sounds so endearing, though you're more focused on helping them pronounce it correctly.  These are all brief moments where you are witnessing the growth of your child.  These moments are fleeting.  They don't exist forever, because eventually they grow out of them.  They don't find the same jokes or silly faces funny, they figure out the round peg fits in the round hole, and their word pronunciation improves.  And when you notice those are past, you feel nostalgic.  You wish you could relive those moments.  In that nostalgia, you forget about all the exhaustion that came with the territory.  Maybe the expression is best described as analogous to another expression "the grass is greener on the other side"