Harry Potter and Matilda.
Harry's parents are alive and he has a brother who is said to be the boy-who-lived, Harry is abused and neglected by his parents so he runs away. Matilda finally got sick of the way her family acted towards her that she ran away as well. At age seven both of them meet on the street and decide to stick together.
Harry and Matilda are soon found by a woman called Jess who runs a street gang of unnatural children and runaways in America called the Street rouges, she takes both of them in and trains them with the rest of the children. Everyone who's there calls her 'Mama J'.
Harry is taught how to use a sword while Matilda is taught how to use a gun and how to use her powers.
The Street rouges work and live under a set of rules: Sleep with your shoes on and your bag packed, one person is always to be awake, no one gets left behind, don't trust anyone outside of the rouges, etc. They work as mercenaries.
Years later and the wizarding world suspects that Connor is not the boy who lived and searches for Harry. Matilda's parents have been arrested along with the Trunchbull for child abuse.
Mama J passes away, leaving the Street rouges to care for themselves. They decide to become the watchers of their city, controlling the crime while getting benefits for themselves.
English wizards are sent to get Harry but none of them succeed. The Street rouges go to the American ministry of magic and tell them that they have Harry willingly with them, they say that unless America does something to stop the English from trying to get Harry they will leave which will cause a power vacuum of crime and evil wizards to their city that won't be controlled. The American M.O.M' agree to their terms if the Street rouges help them with some things they can't handle on their own and they'll get paid to do it.