Story Plot help, please help?

I am writing a story were the main girl has a newborn daughter and moves from a small remote beach town in Australia to a large town with lots of people in England. The town she lived in had less then 20 people living there, but was a hot spot for holidays.
The problem is I was thinking of adding in another child a 1 and a half year old as well as the newborn daughter, should I or not?
The main girl is 18-19 years old and is moving to England with her family. I thought of adding the babies as shes from a small town and all that type of stuff.
I also thought of just adding the older son as a little baby can do nothing but then i thought why not add her at a age where she can do something and not just sleep.