The event at the school's hall, from 10am-2pm, will house 35 stalls as well as children's activities including a bouncy castle, pony rides, face painting and a kids' zone.
Mrs Webster said there had been fewer children on the centre's books this year than in previous years, but dwindling numbers was a problem not unique to the Mosgiel facility.
''It is a trend with play centres nationwide.
''The problem is parents have to go back to work, when they didn't previously.''
Mrs Webster said the centre had always had waiting lists but this year had many spaces to fill.
It had 25 families on its books and about 35-40 children attended the centre, she said.
Children under 2 had to be accompanied by a parent.
Mrs Webster said the funds raised would go to the general running of the centre as well as a new outdoor nature area.
The centre employed one full-time staff member who was there every day and two part-time staff members who were there every second day.
It was government-funded and charged minimal fees so the centre's main expense was paying teacher wages, she said.
Other costs included power and phone bills and resources such as materials.
