I would suggest talking to the school board. It may be very possible to get all your children enrolled in that school. Express your concerns of convience and security. It's security blanket for your 4 year old to be able to recognize familiar faces such as her siblings and its more convenient for you to beable to have all you children in one school for timely responses. There are forms that the school board has that you can feel out. Also, it may be a great idea to have the teacher express her concerns about the benefits your daughter will receive and the necessity of having them all at the same school.
Hope this works out in your favor!
-Debbie Rogers, Realtor