Every body experience is not always same.
Exception always prove the rule.
In childhood I mean in school were innocent, rather happy go lucky days. So these friendships are not lasting.
But you may have some body with you from school to collage as well.
Both ways are possible. There is no hard & fast rule.
Hazrat Ali RA said that poor is one who has no friend.
So it is better you have it.
We do need friends but do not rely too much. Never give your secret to her that if he or she turns and can harm you.
Best friends are your parents; you can share every thing with them.