Find something that your child excels in and give him/her more opportunities to perform n excel. example you realise your child is very good at sports. let him/her join some sports club or find time to let your child attend lessons your coach your child on your own! Allowing them to pursue what they are good at helps to build self-confidence. at the same time, remind them that if they put the same amount of love and effort into something else, they can also achieve good results
Children need constant encouragement. Example if your 8 yr old can remember a new word you taught him recently and used it in his/her conversation with you, heap praises for his/her good learning attitude and good application! If you child uses the word wrongly, praise him/her for trying and give them the right answer. Ask them to try using the word again and if they get it right, heap praises again "wow! you remember that word mummy taught you! Try to remember how did we use it that time?" or "you picked up that word so quickly! i'm so proud of you!"
Giving your child praises is free of charge. no payment needed. just some attention given to them can boost their confidence alot. And when they make mistakes, dont't scold them. praise them for trying but remember to correct them too.
Once they know that you are supportive, they'll naturally start to be more confident.
If you child is very negative. always saying 'i sure fail', 'sure die one', etc. you need to ask them 'why do you tink that way?'. making them tink about the reason helps them to realise that sometimes their worries are groundless. if they give you loads of excuses and you are baffled, just tell them that you belive in them and that's more impt than anything else.