Ebullient

ebullient \ih-BUL-yuhnt\, adjective:
1. Overflowing with enthusiasm or excitement; high-spirited.
2. Boiling up or over.

"The children were ebullient about their trip to the zoo."

It also has a culinary connotation:
"Jennifer ran to turn down the pan of potatoes which were boiling ebulliently."

There is also a noun ebullience which is the same thing as ebulliency.

"The children's ebullience about their forthcoming trip to the zoo was immediately evident."

Some opposites of ebullient are downcast, glum, staid, stoic, dispirited, lethargic, and unmotivated.

Waiter, I'll have a portion of ebuillience, please.