Should the cause differentiate adults from children? Adults continue to say they are happy with their own lives despite not being happy with things in general (source).
Perhaps there is one change that started making everyone less happy since 2011, and another change that started making adults more happy, and it cancelled out the effects of the first thing, but not for children.
Perhaps there is one change that started making everyone less happy since 2011, and another change that started making adults more happy, and it cancelled out the effects of the first thing, but not for children.