Whether you're planning decorations or activities, here's where to start. Looking for other themes? See our full themes guide.
Decorations
Blues, teals, and ocean shapes
- Blue and teal balloon 'bubbles' clustered near the ceiling mimic an underwater feel.
- Paper fish, starfish, and seaweed cutouts hung from the ceiling add depth without much cost.
- Blue tablecloths with shell or fish-shaped confetti tie the table setting together.
Activities
Water-adjacent, indoor-friendly options
- A treasure hunt (buried 'sea treasure' in sand or a sandbox) fits the theme naturally.
- A simple fish or shell craft station gives kids a take-home activity.
- For outdoor parties, water balloon or sprinkler games extend the ocean theme physically.
Frequently Asked Questions
Is under-the-sea a good theme for a summer birthday?
Yes — it pairs especially well with outdoor, warm-weather parties, and can incorporate water-based activities if there's outdoor space.
What age range suits this theme?
It works broadly across ages 2-10, with the specific activities adjustable for the group's energy level.
What's a good cake for an under-the-sea party?
A blue ombré or wave-textured cake with a few edible sea creature toppers fits the theme well — see our full cake ideas guide for more general design approaches.