Found a great article, written by a child psychologist about what makes a happy child. Easy advice to follow, and fairly reasonable I would say.
In short - good routine, healthy independence, respect and your heart. Not so much different from what us adults need...
1. They eat on time.
2. They get consistent sleep.
3. They play without instructions.
4. They are allowed to express emotions.
5. They get to make choices.
6. They feel heard.
7. They experience unconditional love.