The original sentence is mostly clear but can be improved for grammar and flow. Here's the corrected version:
During the rain, the baobab soaks up water like a sponge. Its thick trunk and small treetop help it save water for the dry season.
Explanation:
- Removed the comma after "water" because "like a sponge" directly describes how it soaks up water, so no comma is needed.
- Kept the rest of the sentence as it is, since the grammar and meaning are clear and correct.
This version is easy to understand for a 7-year-old and grammatically correct.