Can a child use a last name that is not their original name?

[apaa_4kids]

I was wondering if a child could use a last name that is not legally their name in the state of Ohio? I have a friend who's older children although still minors are not using a different last name but her youngest are using her boyfriends last name. Is that legal? They are using it in school and sports. The biological father is in prison and was just sentenced. They have been through a lot. My friend told me her therapist told her that if the child wanted to they could and it may just be a way of healing for them.

[Patrick]

Thanks for stating you are in Ohio. The minor can use any name it pleases. The problem arises as to whether any documents or actions taken by or for this minor may be invalid and not recognized by the county, the state, the feds or private business. Legally, that person's name must be changed by a Court decree or by use in order for others to rely, legally, on it.