InstaWeld with Unions?

How can I make this work for Unions so not only parts will be welded?

local prev 
local parts = script.Parent:GetChildren() 
for i = 1,#parts do 
	if (parts[i].className == "Part") then 
		if parts[i].Name ~= "Part" then
		if (prev ~= nil)then 
			local weld = Instance.new("Weld") 
			weld.Part0 = prev 
			weld.Part1 = parts[i] 
			weld.C0 = prev.CFrame:inverse() 
			weld.C1 = parts[i].CFrame:inverse() 
			weld.Parent = prev
		end 
		prev = parts[i] 
		end
	end 
end
for i = 1,#parts do 
	if (parts[i].className == "Part") then 
		if parts[i].Name == "Left Leg" or parts[i].Name == "Right Leg" then
			parts[i].CanCollide = true
		end
		if parts[i].Name ~= "Part" then
				parts[i].Anchored = false 
				end
	end
end

In order to get this to work, you just need to check if the parts are BaseParts or UnionOperations (The ClassName for Unions).

The following would replace lines 4 and 19 in your code block:

if (parts[i].ClassName == "BasePart") or (parts[i].ClassName == "UnionOperation") then