I am sure that all the check boxes will be present in a Table. First try to get the row on which you want to check the check box.
ex: you want to check the Check box at Row 5, Column 2
ex: you want to check the Check box at Row 5, Column 2
Code:
Set wCheckBox = Browser("something").Page("something").WebTable("something").ChildItem(5,2,"WebCheckBox", 0)
wCheckBox.Set "ON"