In the late 1980's when the Muppet Babies popularity began to diminish, Jim Henson Productions marketed the Muppet Show gang as teenagers (or pre-teens) under the brand name Muppets Kids. This resulted in a significant series of Muppet Kids children's books and a limited amount of additional merchandise, but the concept ultimately failed to catch on with Muppet fans or the general public the way that the Muppet Babies had.
Here are two soft cover books. "New Kid in the Neighborhood" was published in 1989 by Muppet Press/Longmeadow Press, while "Too Many Promises" was published in 1991 by Muppet Press/Golden Books/Western Publishing.
"Piggy Takes a Dare" is a soft cover book, published in 1991 by Muppet Press/Golden Books/Western Publishing.
Here are two Muppet Kids hardcover children's books (above and below) published in 1992 by Grolier. The covers say "Jim Henson's Muppets" rather than Muppet Kids.
Here is a Preschool activity book with colour illustrations of the Muppet Kids that was published in 2003, more than a decade after the book series, by Bendon Publishing International. Four workbooks were included in the series along with eight different sets of flash cards. Bean Bunny is included as one of the characters in the workbook, and one picture shows that Fozzie has a younger twin brother named Freddie.
The Muppet Wiki site has more information about Muppets Kids products which seems to have included some computer games and a set of four McDonalds PVC figures. Here is the link: http://muppet.wikia.com/wiki/Muppet_Kids
In the mid 1990s Jim Henson Productions started a new campaign to promote the Muppet Workshop as a brand name. Among the most notable products that resulted were the Muppet Workshop figures that were sold at McDonalds restaurants in 1994. Below are all four figures, Dog, Monster, Bird and What-Not in their original baggies.