Danielle is the female version of Daniel Chesser, and was created as a joke referencing how most people believe the child who possesses Freddy Fazbear is a girl. She first appeared in a Children short and later gained popularity and her own fanclub, /r/daniellefanclub. Later, teen and 21-year-old versions of Danielle were made by Kerubii, gaining mass popularity.
Brendan is the male version of Bianca Alves, created after Danielle as a joke referencing how the missing children were most likely 3 boys and 2 girls. He first appeared in the Children Short titled Equality, and later in the short Excitement, he wasn't seen ever since.
His name used to be Brian, but that was later changed due to the name being used for Kenny's brother.
Children Shorts is a series of silly, comedic, non-canon shorts, in contrast to the main, serious comic.
The first short, posted on May 21st of 2016, featured Daniel, who was complaining about how "girly" the animatronic Funtime Freddy looks, relieved he wasn't going to be the one to possess him. This is also Funtime Freddy's first appearance in the Children franchise.
The second short, posted on May 23rd of 2016, featured Bianca, who found the room in which the comic creators plan and draw everything, the room included the plans for the deaths for each of the 5 missing children, causing Bianca to find out she dies by throat slicing.
The third short, posted on July 28th of 2016, featured the kid version of Danielle, complaining about how she was turned into a girl, insisting to still be called Daniel.
The fourth short, posted on July 29th of 2016, featured both the now-female Daniel and Bianca, with the latter trying to convince Danielle to get used to being a girl.
The fifth, posted on July 30th, featured Daniel, who was still female, and Bianca, who gets turned male at the end, after Daniel questioned the amount of girls in the group compared to boys.
The sixth, posted on August 1st of 2016, had Francis explaining Charlie the gender change Daniel and Bianca went through, while both of them were getting excited over the Steam page for Sister Location.
Part 161 (April Fools Edition)
On April 1st of 2017, a non-canon version of Part 161 was posted to the FNaF subreddit, as an April Fools joke. It shows Kenny totally breaking character and pointing out Brian's shit, using vulgar language nobody would expect from a kid his age.
The real Part 161 was posted a few days after, on April 15.