Extend a view to hide fields in a form in v7?

For example, I want to hide field "Number of Children" on the employee form. So I see it's field: children, object: hr.employee. I have tried: extend hr.employee //Result XML validation error //Passes validation but returns error when trying to open an employee form1 //Fails xml validation I don't know any of this code and I'm trying to find examples and that's where I got these tests from. Is there no default way to hide fields like with `` and I'm extending the form it will hide that field?