I am fairly certain that we had them in Australia too, although I did go to the UK in April of 1990 so maybe I got them there. I did get a lot of ponies on that trip!
I think you did, since Dream Valley originally claimed that the Australian leaflet was "misspelt" for writing Mummy and not Mommy. I assume Australia had the same leaflet as the UK did.
This is coming back to this late but I just got a set of y6 Newborn Twins MIB and there was a charm tucked up by the seesaw in the box. I...don't remember offhand which one it was, I think she's orange. The twins are Tuggles & Toddles/Sticky and Sniffles and the box is US.
I've also seen them a couple of times recently with Peekaboo babies, but not uniformly.
Also, addendum to Hathorcat's list - I'm pretty sure that the difference in release years here (us having certain ponies at different times) meant that some sets differed depending on where and when they were being sold. The Loving Family Ponies are chief suspects for Mummy Charms in the UK
I can't get a hold of my leaflet at the moment to check the date but I suspect they were here around 1989-90, which is a bit later than the North American year 6.