The cousin info has been taken from slo_bro's faq over at game faq's with his permission. I did not write this, I'm merely expanding the reach of this info. Enjoy.
That being said, the way this game was designed makes it a bit difficult to write up an exact how to get there guide as the levels you get are totally random. Pics coming soon!
TUTORIAL - Mouse Stage
June - walking around the perimeter
Prince - walking around the perimeter if you play as June
SHIMANO HOUSE - indoor area with the Shimano kids and with Ace
Turtle Stage Eternal, Turtle Stage, Royal Monument Stage
Ace - a mouse chases him around the floor
Ichigo - in the dresser drawer in the girl’s room
JOUSHIMA VILLA - indoor area with two guys sitting around & with a masked cat
Turtle Stage Eternal, Panda Stage, Elephant Stage
Shikao - at the end of a long ramp of books and fishing rods
Huey - carried by one of the circling angels
MODEL SHOP - indoor area with a guy polishing a fish statue and with Havana
Turtle Stage Eternal, Octopus Stage, Polar Bear Stage
Havana - rolling a donut under the table
Colombo - hiding behind the potted hydrangea
MAPLE TOWN - snowy, day into evening
Canary Stage Eternal, Cat Stage
Miso - in front of a campfire by the rink bleachers, before 75cm barrier
Norn - wandering around some trees in the corner of the shrine square, beyond 75cm barrier
OAK TOWN - day into evening
Canary Stage Eternal, Cheetah Stage, Whale Stage
Shy - walking around in the pool, before 75cm barrier
Kuro - onstage with the colored ninjas, beyond 75cm barrier
SAKURA TOWN - evening into night, lots of drunks staggering about
Canary Stage Eternal, Canary Stage
Lucha - on the counter inside the restaurant, before 75cm barrier
Twinkle - in the audience at the matador show, beyond 75cm barrier
STRAWBERRY CITY - day into evening, with a golf course
Gold Bug Stage Eternal, Gold Bug Stage
Odeon - on top of a boat by the mall, before 4m barrier
Velvet - running around, beyond 4m barrier
MELON CITY - snowy, day into evening, with racetrack
Gold Bug Stage Eternal, Dolphin Stage
Opeo - sitting at a desk at school inside the building, before 4m barrier
Signolo - on the playground in a crowd, beyond 4m barrier
BANANA CITY - evening into night, with zoo
Gold Bug Stage Eternal, Crab Stage
Kinoko - on the side of the hill, before 4m barrier
Mu - on a flat hill with a big cat and a centaur, beyond 4m barrier, get him quickly once you’re on the hill or he will disappear
RADISH LAND - evening into night
Cicada Stage Eternal, Beetle Stage Eternal, Cicada Stage
Can-Can - running in circles atop the hill, before 30m barrier
Foomin - sitting in the palm of the Buddha statue, beyond 30m barrier
POTATO LAND - day into evening, with donut-Rookie Ban-Ban
Cicada Stage Eternal, Beetle Stage Eternal, Beetle Stage
:
Ban-Ban - in the wrestling ring by the beach, before 30m barrier
Nickel - inside the baseball stadium, beyond 30m barrier
ZUCCHINI LAND - snowy, night into day, you start in the water
Cicada Stage Eternal, Beetle Stage Eternal, Peacock Stage
Dipp - standing on the town atop the square hill, before 30m barrier(climb a waterfall)
Slip - inside the Parthenon, beyond 30m barrier
RICE STATE - day
Peacock Stage Eternal second area when you start in RADISH LAND
Nutsuo - on a tiny island surrounded by whirlpools
Peso - next to the Ferris wheel
Macho - standing on top of Red Oni Isle
CORN STATE - evening
Peacock Stage Eternal second area when you start in POTATO LAND
Marny - fighting the two-headed monster
Hans - running back and forth across the long bridge
Lalala - riding a brontosaurus on the plains
WHEAT STATE - night (snowy)
Peacock Stage Eternal second area when you start in ZUCCHINI LAND
Paula - talking to Queen Natasha the penguin
Marcy - hobnobbing with the thunder god
Nik - riding a tornado
SUNFLOWER CONTINENT - the big time
Royal Monument Stage last area
ALL the presents, cousins and objects of the 70m-500m area you start in, plus:
Drooby - on a rising and sinking island, must have started in Rice State
Odeko - carried around by the dragon, must have started in Corn State
Pokkle - walking on a rainbow, must have started in Wheat State
NOTE - Only one cousin will be available, depending on where you started. To get the other cousins you will have to play the whole stage over again.
Themed Stages
ANT STAGE
SHIMANO HOUSE (EVENING) - Sweets stage
Honey - atop a slice of cake on the table where you start
Daisy - grazing on the lawn, must be fairly big to pick her up
CRANE STAGE
PERSIMMON CITY - Age stage
Kenta - standing on some rocks
Fujio - sitting on a storage shed near the bus
GORILLA STAGE
BAMBOO LAND - Rocket stage
Miki - riding the skyway gondola
Jungle - near the Christmas trees
CHAMELEON STAGE
BIRCH TOWN - Requests stage
Beyond - in a small drainage ditch at the edge of the pool, before 80cm barrier
Nai-Nai - tossed out of box in the square up the steps, beyond 80cm barrier
CAMEL STAGE
TRUFFLE DESERT - Money stage
L’Amour - carried around by the eagle
Johnson - riding the camel, be at very least 2m before you try to pick him off