I check for new opinions on Laburnum every year within various woodworking disciplines and so far the attitude amongst pros has always been it's safe especially after a good finish has been applied. But there is always a niggling doubt.Most turners will use it for bowls, a lot of spoon carvers limit it's use to non wet spoons like coffee or salt spoons. I have made a few spoons but sell them as decorative spoons, giving folk the info to decide for themselves. I agree with Robin though that it not worth the effort for food. But it is my favourite wood for carving owls the grain can is perfect for feathers. Not all carving has to be utilitarian, owls are easy to carve and are one of the first things we encourage children to carve. If it must be a spoon , think decorative like a Welsh love spoon.
As to it being hard to carve when it is seasoned, I hear this said of a lot of woods , but find as long as my tools are sharp in a lot of ways its easier . Laburnum splits very easily, and the best way to stop this is to season it.It also means that the finish you get straight from a knife or tool is fantastic.
There are good reasons to work green wood, ease of carving is not always the main reason .
Whether a wood is toxic is far some black and white. Often most people have no problem with woods like Laburnum, Yew or Eucalyptus. Yet the dust from Yew on my skin now effects my breathing, it never used to. A turner friend having worked in wet and seasoned yew for 40 years sudden thought he was having a heart attack, it was the Yew.There is a spoonmaker who having used Eucalyptus for years had a similar experience. For me there are plenty of uses for these woods other than Treen. I hope you have fun with your wood, a friend of mine cut down a Laburnum in his garden to protect his kids and burnt it. He has been kicking himself ever since.