An explanation of the joke for everyone who's not German but curious enough to check the notes:
The puppet in the middle is called "Das Sandmännchen" in German, a diminutive of "the Sandman" - which is obviously where the idea of placing him on a poster of the new Netflix show Sandman based on graphic novels by @neil-gaiman comes from.
Das Sandmännchen, having started airing in 1959, is the longest running TV show in the world (according to Wikipedia). It airs a ten minute episode every evening just before 7 pm on the German public broadcasting company's children's channel (used to be elsewhere, also historically there were different shows for Eastern and Western Germany). In each episode the Sandman arrives to put sleep sand into children's eyes to make them sleep peacefully, but they beg him for a story first (in song). That story is usually animated, featuring a number of recurring characters such as Pittiplatsch and Schnatterinchen or curious Piggeldy and his big brother Frederick (both pigs). After the story the second verse of the song is sung and it's time for young children to go to bed. You can assume that every German under the age of 50 or 60 watched Sandmännchen at some point.
In place of the other Sandman characters there are other popular characters/moderators from the children's channel.
Starting on the left we've got
Beutolomäus: the big bag - associated with Christmas, he was a bag for in which Santa Claus (or rather the German Weihnachtsmann) stored the presents for the children. He came alive rather by accident and is kind but rather sceptic. Also from the notes seems to be either loved or nightmare material
Pittiplatsch: from Sandmännchen stories. Pittiplatsch is one of the oldest recurring characters (been around since the 60s) and is a kobold. He is a bit of a prankster, makes mistakes and tends to end his episodes promising to be really good in the future. He shares his stories with a yellow duck called Schnatterinchen, who tends to be well behaved and helps when Pittiplatsch's mistakes have consequences.
Ralph Caspers: A host of science shows for children who want to learn stuff. He has been presenting the "Sendung mit der Maus" since the late 90s but most of us 90s kids probably primarily associate him with Wissen macht Ah!, a show he presented with Shary Reeves in the 2000s and another female host (Clarissa Corrêa da Silva) later, but very recently they announced he would stop. Wissen macht Ah! usually had about five different topics with some connection in a storyline around it that were explained in short films between presentation. Memorable storylines include that time Ralf got eaten by a werewolf or that time they got lost in a jungle behind a red door in the studio and found Ralf's skeleton at the end of the episode.
Bernd das Brot: A depressed loaf of bread who does not want to be here or do this. He's a cult classic. Most of his time on air is spent trapped in a white hell void being forced to act out short sketch comedy while there is no programming on air between 9 pm and the early morning. He also had his own show for a while (which he did not want to do either).
Willi Weitzel: Host of Willi Wills Wissen (Willi wants to know). Another teaching show, usually focused on one topic for 25 minutes. Topics tend to focus on what it's like to work a certain job, or to be homeless, in a wheelchair etc. The show was cancelled in 2010, as Willi wanted to focus on other projects.
Pumuckl: A small kobold who lives with a carpenter, Meister Eder, and plays all sorts of pranks. He was caught by the carpenter when he got stuck on some glue and is not allowed back to the other kobolds because of it. The book series was published in the 60s, based on a radio play, and of course we are referring to an animated tv show here.
Peter Lustig: another science show host, the show was called Löwenzahn (Dandelion, like the flower). He lived in a blue construction trailer and was replaced by Fritz Fuchs a few years ago. Peter Lustig presented the show from 1981 to 2005. Usually the plot shows some topic/question that is then answered in a number of videos, interviews and even songs occasionally. An episode takes approximately 25 minutes. The title melody is quite memorable too.
Notably missing according to notes: Die Maus, a big orange mouse from another science show on Sunday mornings. (Die Sendung mit der Maus - the show with the mouse)
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