The Children's Museum of Sonoma County officially opens its doors Saturday, though mostly visitors will be sent right back outside into a creative garden area that forms the first phase of the long-awaited facility's construction.

Expected rain could hamper or delay the experience somewhat on Saturday morning, though forecasters said the storm should relent in the afternoon long enough for youngsters and their parents to experience what preview audiences already know: Life is getting a lot more interesting for the area's little ones.

"The feedback has been very positive," said fund development staffer Kristyn Byrne. "I'm just excited that people understand what we're doing here and see the value that we're going to have in the community."

In the nine years since museum founder and chief executive Collette Michaud and a handful of other moms first dreamed of a establishing a creative, stimulating place where kids could explore how the world works, hundreds of children and families have had a glimpse at what they had in mind.

The Museum on the Go has taken mobile exhibits to public events around the county. Several events also have been held on the permanent site since 2011, along with a rolling series of soft openings over the past month.

But Saturday will be the first real opportunity for the public to experience the museum's sizable outdoor area, which provides a surprising range of activities — from climbing and building to splashing around.

Crews at the Santa Rosa facility were intently putting the finishing touches Friday on the museum lobby and on a series of water tables outside that invite interactive play with hand pumps, tubing, hydroelectric energy production, and a variety of other forces that exhibit the many ways in which man interfaces with water.

Cascading water tumbled over boulders in a naturalistic stream-bed, planted with natives species near a wetland below a planked boardwalk.

There's a farm in the works with a real 1940s tractor to play on, a working windmill and a produce market where young visitors can shop.

Across the way a reconstructed farmhouse includes an event room and a light and airy art studio where kids can paint right on the window. The water tables were created by a Richmond design and fabrication studio called Scientific Art Studio, with the idea "that the museum, over time, develops additional activities," studio director Ron Holthuysen said.

Holthuysen's crew also designed components that illustrate the life cycle of a caterpillar and provide the theme for what's called Mary's Garden exterior to the museum building. Mary — aka Mariposa, or butterfly in Spanish — starts off as a large caterpillar that provides a kind of cage-like cave for visitors. Then, she experiences life as a chrysalis that youngsters can get inside, before ending up as a butterfly atop a large tower. Children can make her wings flutter by cranking a wheel.

Construction continues on the indoor Science and Imagination Gallery, set to open this fall.

Even outdoors, the museum is still evolving and not quite finished, though Michaud suggested that simply extends the excitement to subsequent visits.

Byrne said she's already seen families at preview events faced with toddlers who just plopped down and refused to leave.

"The parents are frustrated," she said, "But — I'm sorry — that's exactly how I want them to feel. I want them to want to stay."

Weather permitting, the museum will be open from 9 a.m. to 5 p.m. Saturday. All children must be accompanied by an adult at all times.

The museum will close if rain becomes too heavy, but anyone already admitted will be provided a pass to return at a later time.

The museum, at 1835 W. Steele Lane west of the Charles M. Schulz Museum, will generally be open Friday mornings, Saturdays and Sunday afternoons through May 31, when its hours will expand to Tuesday through Sunday.

Admission is $7 for everyone over 1 year old, though a variety of memberships are available. About 420 mostly family memberships already have been sold, Byrne said.

More information is available at www.cmosc.org.

(You can reach Staff Writer Mary Callahan at 521-5249 or mary.callahan@pressdemocrat.com.)