Woodstock Day Nursery, Farncombe Road, held an anniversary party for current staff and children, parents and former staff on Tuesday and combined it with a celebration for the Queen's Platinum Jubilee.
Owner Anne Shrieves was also celebrating semi-retirement, as she will be stepping back from being in charge.
Anne explained: "I am leaving it in the hands of my two managers, who will be sharing the role. Nothing will change at all. They have both been with me for a while.
"The ethos of family has always been the same but the job is so much more interesting now. Parents do say everybody is so friendly and how happy the children all are."
She opened the nursery in 2000, having completely refurbished a property formerly used by the neighbouring school.
Anne is also chairman of Worthing Business Circle, a networking group which has been running for 16 years and meets weekly at Worthing Golf Club.
Vicky George and Hayley Brown took over the day-to-day running of the nursery on April 1 and said they are delighted to continue to deliver the high-quality childcare for which Anne has been known over the past two decades.
Vicky said: "We are a family friendly nursery and very inclusive. We try to create a family atmosphere. The children can access any part of the nursery all day long, we don't separate them by age groups.
"Our garden is amazing and we all socialise together there. The children know all of the staff so it is just like a family. The older children love it when the babies join them and the siblings can play together."