your 13, a child.
you have so much to look forward to in life, a child would hold you back from reaching your fullest potential.
you have to think, how would you raise this child, where would you both live, can you afford your own health care and your future child's health care, can you afford a car, can you drive yet[no because you are not of age], can you afford to pay rent, food for your child, money for your child, a child costs about $40,000 to raise and that price goes up as that child gets older.
you are 13, you cannot work yet, you dont have your own place, you cant afford your own health coverage for yourself and your future child's, you would not be able to afford the basic essentials to raise a child due to the fact that you bring in no income. therefore, your parents would be the ones who would be the main caregiver providers for that child, and that is not very fair for them.
i think its harmless to have a want of a child at a young age, i think everyone at one point or another has felt the same, but wanting and acting on that want are very different.
babysitting would be good, but having your own is very different. its alot of work, and very stressful expecially at a young age.
my question would be, what is the root to this want of a child for you.
no one just gets the thought that pops into their head thinking

! i want a baby!
why do you have this want, what is going on in your life to make you want this now?
my advice would be, wait until you are much much older.
you are so young, have so many wonderful things to look forward to, so many goals to reach or pursue...having a child now is not the answer or best especially a child having a child hun.
hang out with your girlfriends, go to movies, have sleep overs, girl talks etc. occupy yourself and your mind with different things and activities so the thought of wanting a baby does not come out.
if you need to talk, PM me anytime