My husband who is a stay-at-home DAD was called to serve when our daughter was 4 years old. He wrote and told the judge that he was the primary care-giver and although he couldn't serve at that time, he'd happily do so as soon as our daughter was in school. (He also offered to send me in his place!) The judge denied his request, so he had to be available for the next 3 months (in small town Iowa, we're called for 3 months - rarely do any cases come up, though) and I was ready to take vacation time if he was selected.
We found out a few weeks later that a FEMALE friend who was also the primary caregiver, stay-at-home MOM gave the exact same reason my husband did -- and she was excused.