How do you set parts of GetChildren() back to their original position?

I'm not really sure how to maneuver around this problem, since I'm not that well familiar with GetChildren. One thing that I've tried is saving their position before they were tweened, but it always spits out an error saying "Position is not a valid member of BoolValue"

local Children = Item.Parent:GetChildren()
                for i, child in ipairs(Children) do
                    child.Position = pos
                end