Probably some silly mistake. The error code is Children is not a valid member of model
Children = script.Parent.Model:GetChildren()
script.Parent.Model.Children.Transparency = Variable
Thats just my problem but if the entire code is necessary here it is
Children = script.Parent.Model:GetChildren()
Variable = 0
Des = 0.01
OrDes = Des
function ftrancparency ()
Variable = Variable + Des
script.Parent.Model.Children.Transparency = Variable
end
while true do
wait()
ftrancparency()
if Variable >= 1 then
script.Parent.Model.Children.CanCollide = false
wait (5)
Des = -OrDes
end
if Variable <= 0 then
script.Parent.Model.Children.CanCollide = true
wait (10)
Des = OrDes
end
end

2 comments
I dont really understand, but it worked. Thanks!
If you want to try and think of it in a simplified way, GetChildren() gives you a list of everything inside the object (in this case, the model). You don't want to set the list's transparency, right? You want all of the children's transparency. So, you use a modified for loop to cycle through all of the object's children and change it's transparency.