This time around, the 37-year-old duchess was joined by children from the Anna Freud Centre, Evelina Children's Hospital, Action for Children and Place2Be.
The duchess beamed as she helped the delighted children spot bugs and take part in a treasure hunt.
“These environments enable children to develop skills for life through free play, building their confidence, strength, resilience and social skills," a statement from Kensington Palace read.
"In addition to the physical and mental health benefits of being in nature, spending quality time with parents and carers outside has a valuable impact on children’s early development.
"In the garden, families can explore together and enjoy nature as a playground."