The Abandoned Children joke refers to the fact that many viewers refer to SimpleFlips as "Dad." People have donated calling him dad, telling him to come home, or creating full-on audio clips about how they want him to come back. This does not refer to the song "Dad," which is a song about SimpleFlips' failure to do a Bomb Clip.
It is debatable as to whether or not this joke is based in reality. SimpleFlips has many time denied that he is the father of his viewers, but perhaps he does this to avoid paying child support. There is at least one instance where SimpleFlips implies he is the father of the viewers[1].
Channel Jokes
1, 2 Oatmeal · 200 IQ · Abandoned Children · Adhesive · BUP · Eediot · Fred · Gay Baby Jail · I Can Fly · Ram Ranch · Roxanne · Shoutouts to SimpleFlips · No Cock Like Horse Cock
Stream Jokes
50-50 Grind · Banger · C O O L · Companion P · First Try, Idiot! · Great Entertainer He Is · SimpleFlips Screaming · Speedrunners Hate Him · T-Spin · Garbage
Cursed Bangers
Banger · 1, 2 Oatmeal · Ram Ranch · Roxanne · SimpleFlips Screaming · No Cock Like Horse Cock · I Can Fly
Community Jokes
0.5x A Presses · Aching Tentacles · Bomb Clip · Counter · Dad · Need it as my Ringing Tone · Owless · Press A To Be Gay Today · Pringles Can for $100 · Releasio 64 · TJ "Henry" Yoshi · Toss Your Salad · Unmod Ben · Robot 64
Narrators
Carlos · Harry · Narrator vs Text-to-Speech · SimpleFlips' Narrator
BLJ
BLJ · BLJ the Thwomp's Cock · God-BLJ · IRL BLJ
ROM Hacking Jokes
Green Demon · Invisible Walls · Lava · Lazy Texture Packs · Out of Bounds · Quicksand · Reverse Polygons · Teleportation· Chuckya· Horrifying BUP Abominations
Minus World
Nathaniel Bandy Everytime · Scuttlebug Bandy · Striving for Originality