Student VISA for Kindergarden Children and change the status inside China

My friend She is from Ecuador has 4 years old kids.
They are in China as a L VISA ( tourist) now then decide to study Chinese.

1) is it possible to change to X(Student VISA) from L visa inside
China ? to go to immigration in Shanghai.
2) I think she needs an acceptance letter from the school.
what kind of document you need to issue this acceptance letter ?
3) Her kid is going to the kindergarden now ( i don't know how)
She is wondering if her kid can get a individual X(student) VISA ?
I don't know the kindergarden can issue the acceptance letter for 4
years old kid.
4) Is any minimum age requirement to get a student VISA ?
for example,in U.S over 15 years old ( High School) student can
obtain the student VISA.
with parents's income proof documents - bank statement.
5) I saw the some information that if they study less than 180 days,
that staying as a F visa, If somebody want to stay longer- more than
180 days, can apply X(student) visa.
it means if somebody study short time, cannot apply X visa ? stay as
a L ( tourist) ?

I am sorry it is bit special case and I don't have much kowledge about
Chinese VISA.
you are the expert about student visa if you could give me real
information, I very much appreciate it.

Thank you for your help.