Under the Sea Birthday Party
The whole ocean, not just the mermaid
- Ages
- 3–8
- Runs
- 2 hours
Under the sea is the theme to choose when a mermaid party would leave half the guest list out. It covers fish, octopus, sharks, submarines and divers, which means a mixed group of five-year-olds all find something they wanted. It is also the easier of the two to decorate, because the sea has no single correct colour.
The colour palette
#2F5468 #5C93A8 #7FB8AE #E4D8B8 #C96F4A The running order
| From | What happens |
|---|---|
| 0:00 | Arrivals — magnetic fishing running from the first guest |
| 0:25 | Sort the catch |
| 0:45 | Octopus tag |
| 1:05 | Food |
| 1:30 | Cake |
| 1:45 | Shark and minnows, to burn the last of it |
| 2:00 | Home, one creature each |
Decorations
- Blue and green streamers hung vertically and at different lengths. Uneven is what reads as water; even spacing reads as a curtain.
- Paper fish taped at different heights on one wall, shoaling in one direction. The direction is what sells it.
- A bubble machine if you have one, aimed across the room rather than at the children.
- Sand-coloured paper under the food, with real shells scattered on it.
Food
- Blue jelly with gummy fish set into it, made the night before.
- Fish-finger sandwiches, which are on-theme and eaten by everyone.
- 'Seaweed' — green vegetable strips — which get eaten under this theme and nowhere else.
- A cake iced in blue with a shark fin or a paper submarine on top.
Games
- Fishing game with magnets on string and paper fish with paperclips. Cheap, and it holds three-year-olds completely.
- Octopus tag, where whoever is caught joins hands and the chain grows.
- Shark and minnows across the room or garden.
- Sort the catch: plastic sea creatures pulled from a tub of water and sorted by type.
Favours
- The sea creature they caught in the fishing game.
- A paper telescope they made, if you run that as the quiet activity.
- Shell-shaped soaps or bath fizzers.
- Blue-wrapped sweets in a small net bag.
Where to shop this theme
Invitations, thank-you cards and favours are the strong categories on Zazzle for this theme. Physical decorations are thinner there — buy those locally and spend the budget on the paper, which is the part guests keep.
Invitations
Thank You Cards
Cake Toppers
Banners & Signs
Napkins
Favour Tags
Affiliate links — at no extra cost to you. Prices are from Zazzle as of August 2026 and change without notice.
What makes the difference
- Choose this over a mermaid party whenever the guest list is mixed. Same decorations, no self-selection at the invitation.
- One warm colour — coral or sand — against all the blues, or the room goes flat exactly as a mermaid party does.
- Hang things at different heights. A flat wall of fish at one level looks like a poster; staggered, it looks like water.
- The magnetic fishing game is the best value activity on this whole site: a few pounds of materials, and it runs itself.
Common questions
What is the difference between this and a mermaid party?
Mermaid centres on a character and leans pink-and-teal. Under the sea is broader — fish, sharks, submarines, divers — so it suits a mixed group and boys who would skip a mermaid invitation.
What age suits it?
Three to eight. The fishing game works from three; shark and minnows keeps the seven- and eight-year-olds moving.
Do I need a lot of blue?
Less than you think. Two blues, one green, and one warm accent is enough. Buying every blue in the shop is what makes these parties look muddy.
Can I combine it with a mermaid theme?
Yes — run under the sea as the room and let the birthday child be a mermaid. You get both without splitting the guest list.