The Heart Family Cousins were introduced in 1988 with each set featuring a single li'l friend and some kind of accessory like a potty chair, tricycle, or rocking horse.
Set #5396 and #5397
Set #5394 and #5395
Set #5399 and #5398
Some European releases of the cousins
Here they are deboxed:
Cousins Kevin, Nellie and Kevin
Cousins Honey, Melody and Janet