‘ And this lot was for the remainder of the children of Manasseh according to their families; for the children of Abiezer, and for the children of Helek, and for the children of Asriel, and for the children of Shechem, and for the children of Hepher, and for the children of Shemida. These were the male children of Manasseh, the son of Joseph, according to their families.'
These were in fact depicted as Manasseh's great-grandchildren in Numbers 26:9-32, and as children of Gilead (see Joshua 17:3 below). Family terminology was applied loosely. ‘Son of' can simply mean ‘descendant of' or ‘tribally connected with'. A man ‘bore' tribes as well as children (Compare Genesis 10:15-18). They then all became his ‘children'. Thus these were tribes connected with the name of Manasseh and connected with his descendants. There is an interesting midway between direct family inheritance and tribal inheritance reminiscent of early days.
It may be that Manasseh had a direct descendant named Shechem, or this may indicate Manasseh as taking Shechem under their umbrella and incorporating them into their tribe at a date prior to the conquest, through messengers sent to make early contact with their brother tribe who were not seen as Canaanites. Either is feasible. There was also a town in Canaan called Hepher whose king was slain by Joshua (Joshua 12:17). But duplication of names was quite common without it necessarily having any significance.