It's still vitally important for you to keep working at building your child's confidence throughout these years, especially as school life and friends may give it a sideways knock.
Give praise and positive feedback - your child measures her worth and achievements by what you think of her. "Well done, that was hard, and you managed it" is music to young ears. Reassure your child that it's OK to make mistakes and that it's all part of growing up.
Practise active, reflective listening - listen carefully, repeat what you've heard to make sure you understand and give positive prompts to encourage your child to continue.
Acknowledge your child's feelings - and help her express them verbally.
Criticise behaviour, not your child - it's very easy to fall into this trap, but too much criticism tells your child she's a bad person and is causing things to happen because of her own stupidity. This is very damaging if it goes on for a long time. Be clear that it's an action you're angry about or behaviour you don't like.
Respect your child's interests, even if they seem boring to you - take a genuine interest in your child's friends, and what's happening at school, and comment to show you're listening.
Encourage independence - encourage your child to take chances and try new things. Succeeding gives a huge boost to confidence, and sometimes your child will need to learn by her mistakes. Laugh with your child - never at her.
Focus on your child's successes - swimming, music, whatever she can succeed at.
All the following can damage a child's confidence:
saying you don't love them
saying you wish they'd never been born
insults or unkind remarks
deliberately ridiculing things your child does or feels
cruel teasing and sarcasm
endless nagging
aggressive shouting and swearing
None of us are saints and we all sometimes say something and immediately regret it. If this happens, it's best to admit this to your child. Say: "I should never have said that. It was an unkind thing to say and I don't mean it. I'm just tired." Then have a cuddle and make up.