I'm 13 and i want to start babysitting. How do i make someone take me seriously? **READ DEATAILS!!!**. ?

I've been a mother's helper for about three years now. The woman i have been working with is my mom's best friend (literally, they have been best friends since 7th grade, they r in their 50's now) and I have been working free of charge with her because she is also a close family friend and when i was first starting, i was too young to be earning money. But my birthday is coming up in october ( i'm actually only twelve btw (shhhh) but i'm turning 13 so that's only three months away so i might begin in the school year IF PEOPLE TAKE WE SERIOUSLY. im very mature for my age. the the woman i work for has two children (a 6- month old boy and a 2 year old girl) i have been taking care of the 2 year old since she was 3 months and i have been taking care of the boy since he was two weeks! i'm not saying that they have to let me babysit a child at a very young age, i mean i can take care of a five year old because my cousins and my neighbors r around that age too and i get along very well with them and their parents. my neighbor moved here when she was five (she's like 7 now) and she went to go visit her grandmother and her grandmother asked her what was her favorite part about the new place she moved to, so she thought for a moment and then she responded with MY NAME!!! her mom told my mom who told me and i was like AWWWW!! but anyway, because of my experience with my mom's best friend, i learned how to hold a baby, feed a baby, burp a baby, carry a baby, cradle a baby, lay down a baby, play with a baby /toddler, change a diaper, i know how to control a baby when it's crying/whimpering/whining (feed it or change it's diaper or it's tired and it's trying to fight it so u just lay it down in it's crib and u wait a little bit, usually it stop crying but might just want to be held.) thew only thing i dont know how to do is give a baby or toddler a bath. i'm afraid of doing that anyway. I also know CPR and the heimlich maneuver on babies and young children (learned it in health cl last year) i did have a certificate from the american red cross but it expired a couple months ago and i have no idea where it went because it was smaller than an index card so that's out of the question, but i still know how to do CPR and the heimlich maneuver, i just don't have a certificate saying that im certified. i also know that i have to get medical info (numbers, if the child is allergic to something, ect.) the times i have to feed a child, where the toddler is allowed to go, stuff like that, but people will NEVER take me seriously just because of my age!!!!how do i make a person take me seriously!!! plzz help!!