Here are the corrected phrases and short, easy rules to help you understand why they changed. I fixed hyphens, redundancy, and punctuation so the list sounds natural.
- Round target
- Oval-shaped swing chair (clearer than "oval swing chair")
- Globe ("spherical globe" is redundant; a globe is already spherical)
- Square map
- Rectangular flag
- Cube-shaped street organ (you can also say "cubic street organ," but "cube-shaped" is clearer)
- Triangular sign
- Diamond-shaped kite (use a hyphen, not an en dash)
- Pyramid-shaped tent
- Cylindrical crawling tunnel
- Trapezoid-shaped boat (or "trapezoidal boat")
- Star-shaped piñata
- Hexagonal spider web
- Heart-shaped glasses
Short rules for a 10-year-old:
- Use a hyphen when two or more words work together as one adjective before a noun: "heart-shaped glasses," "star-shaped piñata."
- No hyphen for single-word shape adjectives: "round target," "square map."
- If the shape word comes after the noun (after a form of "be"), you usually don’t hyphenate: "The glasses are heart shaped."
- Avoid redundancy: don’t say both a shape adjective and a noun that already means that shape (for example, say "globe," not "spherical globe").
- Use a hyphen (-), not an en dash (–).
- Be consistent: either write items with lowercase (if they’re fragments) or capitalize each item the same way.
If you want, I can rewrite the whole list in sentence form, make them lowercase, or make them into labels for a picture. Which would you like?