We don’t know exactly what Jesus called his mother when he was young. The Gospels don’t include any stories where the child Jesus addresses Mary directly, so we can only guess. It seems logical to assume that the young Jesus would have called his mother the Aramaic verison of “Mommy” or “Mama” (Aramaic was the language spoken by Jesus and his community).
We have a little more to go on when Jesus is an adult. In the Gospels, there are two separate occasions when he addressed his mother as “woman” (both at the Wedding at Cana in John 2:4, and while Jesus is on the cross, in John 19:26). Though this sounds harsh to modern ears, it was actually a term indicating respect.