I would say it's the same occasion too. As Incas points out there are lots of children in your picture Umbrellagirl and one of Diana's engagements that day was to go to a Pre-school Centre.
Here's (a rather fuzzy) full length picture (Photo: Prive magazine) This picture always makes me laugh. There were obviously horses around that day!!
She didn't wear that dress often did she? There are pictures of her wearing it in June 1992 in the book "The Diana I knew" by Mary Robertson (Diana is posing with Mary & her children). I also have this picture from sometime in the summer of 1991. Here she is wearing different earrings from your pic Umbrellagirl and also no necklace. I would love to know the date or even the occasion, if anyone knows ...