Both girls' and boys' voices change as they go through puberty, and they are changing as children grow up too, simply because everything is growing.
The changes for boys are more marked than for girls because when they are somewhere between 12 and 14 (generally) their larynx begins to grow extraordinarily fast, 7 times faster than anywhere else in the body. Just imagine if that happened to their nose?
The huge changes occuring in the voicebox or larynx relate to the size of the structures there. The vocal folds are attached inside the larynx from front to back, and the cartilage of the structure grows front to back and side to side. The boy's vocal folds have to grow as well, and the boy loses his high voice because the longer, thicker vocal folds make lower sounds.
Little girls don't sound like women, so there must be some change around puberty for girls too. The larynx does grow, but not so markedly as with boys. Girls sometimes go through a phase where their voices get breathy, and some researchers think that those changes are something to do with pubertal changes.
You have a long time to wait for all this, and please don't worry about it. If you enjoy singing, just go on doing that.
Hey Elizabeth , it's Alex I can't wait to come over, my grandma's got her whole house packed up and gone . I promiss you I'll come over every other week . We've got to find a song to sing !!!!!