Thanks Eva,
I am pretty sure that the child of William Matthew is a grandchild of Agnes King. It took me a while to figure this out- the first William Matthew mentioned in the parish record is the grandfather William King. I believe the second mentioned is his son, William Matthew, and the child is at the foot of William Jr's mother (Agnes King). This for me that my Robert (son of Agnes and William) had a brother named William.
I also know from church records here in Canada that my Robert had two nephews come to Canada, named Robert and James- they may be sons of William. I will definitely take another look at the Fife historical society site. I am planning a visit to Markinch this summer, and I'm hoping to meet up with anyone researching the Matthew/Matthews while there.
Thanks for your help!