Happy Birthday, Maisy! is based on characters created by the British author Lucy Cousins for her picture books series, characterized by bright solid colors and boldly outlined 2D figures and objects.

Maisy, a mouse, is celebrating her birthday with four animal friends; the player is invited to join in by using the mouse to play three classic games and participate in three party activities:
Treasure Hunt - the player helps each character find a special object

Follow the Leader - as each featured character does a dance move, the player chooses who is doing the same thing

Pin the Tail on the Donkey - the player moves blindfolded characters to the donkey game by following audio directions, then drags the tail into place

Make a Birthday Card - Cyril has forgotten to bring a card for Maisy and must make one; the player helps by assembling and decorating it

Prepare Food - Charlie follows his nose to help Maisy in the kitchen; the player assists by dragging various food to it's matching shape on a party platter

Guess the Presents - as Maisy holds up a wrapped present, the player chooses the best match from a set
At the main screen, the player is able to choose to play the story or select from the games at two levels of difficulty; activities can be skipped and the level changed during the game as well. The focus is on shape recognition, comparing, matching, and creative play.