There is no quick fix to building a healthy mental state with our children. Slow steady consistent habits developed in your family can be great boosters for mental health.

Consider:

Affirm the small achievements.
They do not need to be on a large scale but you recognize in your child some simple milestones that they have made. That could be at school, sporting efforts, improved attitudes, showing generosity, demonstrating gratitude etc.
Give them the liberty of talking about issues.
Sometimes we jump in fairly quickly and can place judgement on what they have to say. Just be an effective listener without showing strong opinions and let the conversation flow. You may learn something interesting.
Play and enjoy their childhood.
A happy child who plays often and lives in a world where they can be creative and free show a greater ability to be less stressed throughout life. We all need a good childhood. Play with them.
Gradually build their independence.
From birth, a child is working to be more independent. Your support in giving them small opportunities as the years go by, will give them personal satisfaction in managing themselves. As they grow in independence, they feel emotionally in charge and ready for more challenges. They accept failure more easily and see it as a learning curve.
Let them think critically
A critical thinking child develops strong emotional independence. Talk frequently to your child and let them ask questions often. Guide them in thinking about optional viewpoints and keep their minds open to new ideas. A closed mind is dangerous

A child who learns to inquire about life is not frightened about the challenges it offers. In fact they invite them.

“Those foundation years need ongoing nourishment and enrichment to keep developing good mental health.”

— Gail J Smith