Correct sentence: Birds and animals fill their tummies with berries before the cold winter.
Other good ways to say it:
- Birds and animals eat lots of berries before the cold winter comes.
- Birds and animals gather berries to eat during the cold winter.
Why change it?
- We add the before cold winter because we mean that particular season — the cold time of year.
- "Fill their tummies" is friendly and fine for a child to use. If you want a different word, use eat lots of (means the same) or gather (means they collect and save food).
Try saying each sentence out loud and pick the one you like best!