Keeping the habitat clean. Raising the tadpoles. Your family is a delicate ecosystem.

No wonder you’re reluctant to add one more microorganism to the sphere.

Silence pleas for a puppy with EcoAquarium, home to two African dwarf frogs, a bamboo shoot, and a snail.

At a mere four by four by five inches, each tiny aquarium is its own little world. The special “living” gravel is a natural filtration system; the water needs to be changed only every six months. Mr. Snail stays happy by eating the algae, and the frogs need to be fed only twice a week.

Park the aquarium in the little one’s bedroom; he’ll be thrilled with his new friends.

And you’ll be jumping for joy.

Available at Henry Bear’s Park, 19 Harvard Street, Brookline (617-264-2422); 685 Mass Avenue, Arlington (781-646-9400 or henrybear.com).

GO
Marshfield Fair
What: Carnival rides, music, games, shows, agricultural displays, and much more.
Why: Step right up.
When: Today-Fri., noon-10 p.m.; Sat. & Sun., 10 a.m.-10 p.m.
Where: Marshfield Fairgrounds, 140 Main St., Marshfield (781-834-6629).

STRETCH
Intro to Yoga for Pregnancy
What: Learn basic, belly-pampering positions that you can do while you’re preggo.
Why: Take a breather.
When: Sat., 11 a.m.
Where: Crunchy Granola Baby, 72 Washington St., Salem (978-741-0800).

PLAY
Kids Day at Winslow Farm
What: Arts and crafts, games, face painting, pony rides, and a chance to meet the farm’s rescued animals.
Why: Where a kid can be a kid.
When: Sat., noon-3 p.m.
Where: Winslow Farm Animal Sanctuary, 37 Eddy St., Norton (508-285-6451).