"As a performer you know the minute you stop connecting with your audience.
"The response with children is immediate and it's totally honest," she says.
The Auckland-based actor and director is back in Dunedin, her home town, directing her play, The Frog Prince, which opens at the Fortune Theatre on Tuesday.
It's one of several productions her company, Phineas Phrog, has opening around the country for the school holidays.
The Bubbles and Mustard Show opens at the Fuel Festival in Hamilton the same day as The Frog Prince here, Twisted Tales is opening in Invercargill, The Little Mermaid opens at the Bruce Mason Centre in Takapuna to celebrate the company's eighth birthday, there are five daily shows at the Auckland Zoo, a school holiday story-telling show, and various birthday parties that request entertainers, she says.
"I have to remind myself to stop working at night and in the weekends, but I do love it, and when it's your own script as well you want to give so much more to the production, so it benefits in the long run, even if I have a few too many late nights and too few weekends."
She not only directs, acts and manages the company, she also writes the scripts herself - although she has staff who help with organisation during busy periods and a large pool of actors to draw on.
She is enjoying directing this joint production with the Fortune because she does not have to worry about ticket sales and advertising, although as soon as the show opens she has to leave for Hamilton, she says.
Somerville grew up in Dunedin and went to drama school in London, but being a sixth-generation Kiwi, could not get a visa to stay and work there as she wanted to.
After working for a year at the Fortune in the late 1990s, she went to the Court Theatre in Christchurch where she fell into children's theatre, she says.
"I started doing grown-up plays on the main stage, but they had a strong children's programme going as well so I started performing in that, often doing children's shows during the day and grown-up shows in the evening - working very hard."
She would like to change the general perception that acting in children's theatre is somehow lesser than adult theatre.
"It's a wonderful training ground, but there's a lot of older, more experienced actors who could benefit from it as well."
Writing and performing good plays for children requires working on several levels, she says.
"I try and really layer the shows.
"I put in lots of physical comedy and colour and music for the littlies, then you add the slapstick and verbal gags for the older children, then we add another layer of double entendre and contemporary jokes for Mum and Dad because not only do we want them to enjoy the experience, we want them to come back next holidays or next time."
She also emphasises audience participation in her plays.
"The children get to jump up and participate and feel they are helping the actor's journey or influencing the outcome of the play in a positive way.
"And it's also the active use of the imagination - things you can do at home as well.
"We get them to pretend to be fire-breathing dragons, flapping their arms, or bluebells going ding dong in the breeze."
The Frog Prince is based on the traditional fairy story, but with a modern twist.
The golden ball that disappears down the well is a golden rugby ball, and the princess wants to be in her school's first XV.
The frog helps her to her goal.
"There's music and singing and lots of the elements of pantomime and audience participation.
"It's very physical and full of beans. The actors will be hot and tired by the end," she says with a laugh.
See it:
The Frog Prince, written and directed by Sarah Somerville, opens at the Fortune Theatre on June 29. It features Nayda Shaw Bennett, Patrick Davies and Mark Neilson.
