Learn Turkish: On dokuz bebek tok. - Nineteen babies are full.

Turkish forms numbers from 11 to 19 simply by placing the smaller number right after ten. You say ten (on) followed by nine (dokuz). There is no word for 'and' between them, just on dokuz.

Why is the word bebek (baby) singular when there are nineteen of them?

In Turkish, when you use a number before a noun to state a quantity, the noun always stays in its singular form. You say on dokuz bebek (literally 'nineteen baby'), and never add the plural suffix to make it on dokuz bebekler.

Where is the word for 'are' in this sentence?

There is no separate word for 'are' here. In simple sentences describing a state, 'is' or 'are' is often just understood by the listener. Placing the adjective tok (full) right after the subject naturally translates as 'are full'.

Does tok mean 'full' like a glass of water, or 'full' like after eating?

Tok specifically means 'full' in the sense of a person or animal having a full stomach and not being hungry. If you want to say an object or a room is full, you use a completely different word: dolu.