Words for children in VN - guidance please

[rukkhamula]

Chào các bạn

I would like some guidance on which words to use for child/children in VN. I have so far found these words:

trẻ con

trẻ em

đứa trẻ

con

con nít

There seem to be a lot of words for a child or children as part of a family group (eg youngest/oldest child), but I'm really looking for the most general all-purpose word for a child or children. For example, how to say:

1) There are some children playing in the street.

2) Is this your child?

3) Children are the future.

4) Every child has the right to healthcare and education.

5) How many children do you have?

Also, is there an informal word for a child or children - the equivalent to 'kid/s' in English?

Any guidance on usage would be appreciated. Thanks!