Here are suggestions for completing the sentences with appropriate words derived from the given prompts:

1. **playful** (adjective form of "play")
2. **active** (adjective form of "act")
3. **athletes** (noun form of "athlete")
4. **behavior** (noun form of "act")
5. **jumping** (gerund form of "jump")
6. **childhood** (noun form of "child")

So the completed sentences would read:

1. playful
2. active
3. athletes
4. behavior
5. jumping
6. childhood

This keeps the context relevant to the theme of play and learning through activities.