Do children have to apply for citizenship before turning 18?

[Jackolantern]

I donot see anything on N-600 form mention about child name change. I wanted to short my first name and middle name of child.

There isn't any option for name change in the N-600 process. If you want a name change for your child it has to be done totally outside of USCIS in a separate court process. Contact your City Hall to get information on the forms and procedures and which court to file the paperwork.