And the baby ponies get smaller and smaller! The Newborn Twins were Hasbro's latest introduction into the pony family tree, and they were tinier and cuter than ever before. Some twins, like Milkweed and Tumbleweed and Rattles and Tattles were identical in design and differed only in pose, making them tough to tell apart, whilst the others had similar or reversed colour schemes.
The UK issue is kind of confusing. I know we definitely had Sniffles and Snookums and Nibbles and Dibbles, with Sniffles (lavender) being projected as a boy pony (the only ever male unicorn, but then, in the USA, Sniffles was a girl, so :P). The Hasbro list also includes Jangles and Tangles for the UK, as does their promotional booklet picturing the ponies intended for 1987. (See left - thanks to Pranceatron for this scan!!)
However, between the development and the store, something changed, since Jangles and Tangles are not pictured on the insert with the other pair of twins - see below. Though shown in this picture with their correct 'big' accessories, I cannot be certain how accurate the colours of the other accessories are - you can compare some to the picture of Sniffles and Snookums in UK box at the foot of the page :) Please also note that my Dibbles' hair is faded to white from pink.  Nibbles and Dibbles had an aqua bassinett with a yellow top (NOT pink as some sites have suggested - this is identical to MIB US Dibbles and Nibbles sets I've seen online, and to the set I have in Italian box, so it seems their accessories were universal) and Sniffles and Snookums had an aqua and yellow stroller (again, I believe this to be universal). Apparently Nibbles and Dibbles began life as "Dimples and Ruffles" - since some sets (maybe all!) were sold with stickers bearing this name (thanks to Lady Guinevere for this information and for the above scan!!)