For a playful, but firm, approach:
* Whimsical: Suggests a playful and imaginative approach, but also a sense of order and structure.
* Lighthearted: Implies a sense of fun and ease, but also a willingness to enforce rules.
* Disciplined: Highlights the strict side, but with a hint of playful energy.
* Fun-loving: Emphasizes the playful aspect, while still suggesting a sense of boundaries.
For a more nuanced, contrasting approach:
* Paradoxical: This highlights the apparent contradiction between playful and strict.
* Contradictory: Similar to paradoxical, but emphasizing the tension between the two qualities.
* Unorthodox: Suggests a playful approach that doesn't follow traditional norms, but still maintains a sense of structure.
For a specific context:
* Playfully strict: This directly combines the two words, offering a clear and concise description.
* Strict but playful: Emphasizes the order first, followed by the playful element.
The best word to use will depend on the specific situation and the desired emphasis.