Hi Francesca -
I think you’re getting curious about what it’s like to have babies, and judging by your dream, you may be impatient to get going! In the dream, you are jealous that your mother, who is older, is able to have this new baby, while you, being 16 years old, only get to “look after it.” I doubt that you really want to have a baby right now - with all the responsibility it entails - but you may be feeling jealous of your mother’s independence. She’s an adult - and can make her own decisions! If your Mom did have a new baby, it’s also possible that you might be jealous of all the attention it would receive in the family, as newborns require a lot of care.
It’s interesting that the baby turns into a cat, who then runs into a busy street. Cats frequently symbolize babies in dreams (see some of the dreams in the Women’s section, under category heading “Pregnant”). They are about the same size as babies, and we pick them up and carry them around like babies. We also feed and take care of them. The cat running into the street reflects your own concerns for caring for a baby. Young children, as you know, always are a couple of steps away from disaster - they can hurt themselves seriously if you take your eye off them even for a minute. I think your dream shows that you are aware of this responsibility.
It’s natural for women to be dreaming about babies. Maybe in your next dream you’ll be the one who has the baby, and then you’ll really get a taste of what it’s like to be a Mom!