Well, don't be scared, it is almost undoubtedly your period. Have you had any lower abdominal cramps?
When a uterus is just starting up, the menstrual fluid builds up a bit in it, and as it waits, it darkens. There's a saying "brown blood is old blood." A lot of women have the first sign of their regular monthly flow be a few blobs of brownish blood, before a full flow of red fluid begins.
Get yourself some supplies, pads and tampons, so you won't be caught out if it turns into a full flow. Watch the calendar if it doesn't, because in about 28 days, you might have a period if this isn't it.
No worries....sounds like you have started your period....well, this is your first.
Talk with your mother about the situation and she should get help you get the products you need.
Don't be scared dear.