A spoon they can hold
A short spoon they can grip lets them join in. You can load it and let them bring it the rest of the way.
Mess is practice
Expect mess. A spoon is practice, not a standard they have to meet before they get more food.
Load a small amount. A heaped spoon that falls is frustrating. A small one that arrives is a win.
Fingers still count
The spoon does not replace hands. Some of the meal can be picked up. Both are eating.
If the spoon becomes a fight, put it down and let them eat the familiar food with fingers.
You still watch
A spoon does not mean you can leave the table. Stay for the chewing.
Hot food and a waving spoon are a poor pair. Lukewarm is the comfortable temperature.
A sentence you can say
“Your spoon. A little on it.”