The whole party fits in a garden or a front room. Dinosaurs do not need a venue, they need dirt, or something that looks like it.
Bury a few plastic dinosaur bones or shaped pasta in a tub of dry rice or sand, hand each child a spoon and a paintbrush, and let them excavate. This single activity holds a room of four- and five-year-olds for twenty real minutes, which is longer than almost anything else on this list.
Set it up before anyone arrives. A dig site assembled while children watch loses the discovery; a dig site they find already buried keeps it.
Baking soda and vinegar in a papier-mache or cardboard cone, done outside, is the moment every dinosaur party remembers. Do it once, as a group, with an adult pouring — not as a station children run themselves.
Green grapes become "dinosaur eggs". A plate of vegetables becomes "what a plant-eating dinosaur ate for lunch". You are not cooking differently — you are naming the same food differently, and it works.
No. A dig site and a volcano carry the whole party. Costumes are optional and expensive for something the theme does not actually need.
Roughly three to seven. Under three, the dig site alone is usually enough; the volcano and roar games land better once a child understands "pretend".
Part of our guide to Birthday party for one obsession.