I'm in a very similar situation, almost identical, sans kids. I too have this 'struggle'. There's no solution, you're just experiencing life. You're at a stage where you're more safe than you probably had been in the past (I don't know about you, but the 2008 crash really set the tone for my young adulthood). I know I tend to think "I've finally arrived...now what?"

Some combination of suggestion & things that've worked for me:

1) getting a therapist. They will be able to help you work through the feelings a lot better than anyone on HN.

2) don't try to be happy. You can't directly control how you feel like it were a light switch. Aim for contentment and create an environment where you're more likely to be happy. the harder you try to be happy the less likely it is to happen.

3) reduce your focus on work. work is a means to create an environment for you to be happy in. find things outside of work to pour your love and ambition into. Find other sources of validation than work

4) meditate -- and start with guided meditation of some form. do it regularly. it will help you cultivate yourself