Before you plant willow do some research. It is invasive and will grow very large and get into house foundations, sewerage and water pipes. They require a lot of water. If you can grow some in a pot would be best but make sure to sit it on a weed mat so the tap root cannot get out the bottom of the pot and drive it’s way underground.

From my understanding, all willow is safe for consumption. I imagine that small animal toys are made from weeping willow or similar. Roberta is right, they can be very aggressive.

This is from HRS.

Should I give the rabbit items to chew?
Yes. You can give rabbits pieces of the thing they want to chew: their own small towel, for example, providing they aren’t ingesting it. This is especially useful when the attraction is the particular consistency.

Here are some items that are OK for rabbits to chew on:

apple, willow, aspen branches;
pine firewood;
cotton towels
untreated fresh pine lumber attached to cage so it doesn’t move–piece of molding, 1″x2″s, or 2″x4″s;
basket with hay in it–let the bun chew the basket as well as the hay;
compressed alfalfa cubes

Aren’t some woods toxic?
Fruit tree branches, such as, apricot and peach are toxic while attached to the tree but not after they’re cut and dried (a month or more). Lisa McSherry and Rusty Fayter, who package The Busy Bunny baskets, share this research. Another tip they offer for your bunny’s safety is to keep your purchases of imported baskets limited to willow, the only basket material not sprayed with pesticide.