Check for a smile
As parents, we often have a gut instinct that our child isn't happy.
Sometimes it's imperceptible we can't explain why, we just know if a child isn't happy. Does that mean they're “un”-happy? I don't think so.
I believe there is a place between happy and “un”-happy, which can fool the adults around a child into believing nothing is wrong.
Feeling happy and experiencing positive emotions is crucial for children. A 2015 study of boys and girls found a significant positive relationship between happiness and achievement of students, whilst an earlier 2002 study showed that positive emotions do more than simply feel good in the present. Experiences of positive emotions also increase the odds that people will feel good in the future.
Many schools use the Leuven Scale as an indicator of emotional well-being. More information about this scale can be found here. It's a useful measure that is used to assess how well a child (or adult) responds both in terms of well-being and involvement. The descriptor for level 5 - Extremely High on the well-being scale starts with “The child looks happy and cheerfully smiles…”
Smiles.
The best barometer of a child's happiness is the presence of a smile. When the smile gets lost it's a sure indication that all is not well. A child without a smile may not be “un”-happy and they certainly aren't happy.
At the nursery, my eldest son was constantly referred to as “Smiley Al”. He had a wide, beaming smile, which was almost always present. As he moved up through formal education, somewhere along the way his smile got lost.
It was difficult to notice as parents, we didn't immediately spot it. Eventually, in year four he was diagnosed with dyslexia. Almost overnight his smile returned. The contrast, observed by the school as well as at home, was stark. During that year he made the equivalent of 2 years of academic progress.
If your gut is telling you all is not well, no matter how apparently content your child appears to be, check for their smile.