Call the Fremont Unified School District and ask. The phone number for Pupil Services is 510-659-2534. Ask where your child would go the school from a certain address. Ask if there is a waiting list for that school. Many Fremont schools are overcrowded and pupils are sent to other schools in the District.
Here is a link to the school district website page that shows attendance areas. That will give you some idea, but it is best to call the school district.
You didn't give us enough information to give you an answer - is there a specific address you are wondering about? If you want to know what elementary school services Sundale proper - it is Blacow Elementary. Millard services lower Sundale.