I don't think that it can boost their confidence. When they saw that you're sad and crying, they will be upset. Resulting them to become easily angry at things and mad at other things too. It's traumatic for a child to see their parents cry.
I don't think crying in front of your child can do much good. It's important for them to know that you have emotions too, but it's best to stay calm, as you're their source of stability and strength.