Also the problem with not working isn't boredom per se - with enough money anyone can fill their days with pointlessness to keep "busy" - it's sense of purpose and self esteem.
Hobbies and 99% of volunteering roles are too optional.
The catch 22 of work is that most peopleneed to resent having to go a little bit (even if they actually love their job its the obligation of it). The obligation and commitment is what most of us simultaneously hate and need, in order to appreciate the rest of life.
A lot of people go down hill fast when they retire. The early retired are often mentally older than their years. Even if they travel and have hobbies and interests their world's contract after the first heady years and they sometimes become egotistical or neurotic, because what is actually the point, in an existential sense...
Looking after small children gives you purpose and fills your life, absolutely. Your world and self esteem does shrink though - and once they're both established at school you'll be "keeping busy" while they're out of the house, which isn't psychologically good for anyone after a while. Lovely for six months, but not if that's it with no end in sight.
Being dependent on one other person is very psychologically unhealthy for a fit and capable adult longer term. It'll grind your self esteem down without you noticing at first.
Also your DH married a competent, well qualified woman - he sees the convenience of you being at home to do all the child wrangling and admin, and imagines long idealistic holidays - but will you be the same person after ten or fifteen years of being at home?