I’m sure I’m not the only one who does this, and I know we’ve discussed nicknames we give our pets, but what about our kids, grandkids, sibs, whatever?
When my daughter was a baby/toddler, we called her either Poot or Puddin’
As a result, I called my granddaughter Puddin’ Pop, so as not to confuse her mama. 
And I’ve been calling my grandson Sweet Cakes. Maybe I have an unhealthy dessert obsession?
What adorable names have you bestowed upon subsequent generations?
When my brother’s son was born he was named Robert, which sounded too adult to me. I called him “Baby Bobby” and it stuck. The kid is 31 now and we all call him Baby Bobby.
My sister’s youngest son was into older women for awhile. He was 19, dating a 38 year old bartender. Shortly after I met my gf, we hosted a family party. The nephew drank a bit too much and hit on my gf, hard. He has since grown up, but we still call him creepy nephew.
My son, aged 9, was nicknamed Boo Pickle from birth. I have no idea why.
But it also morphed into calling him just “pickle”, or “Mr. Boo.” I still call him Boo sometimes, although I find myself saying Kiddo a lot, too.
My daughter’s pet name was “Kid.” My wife sometimes uses “Kiddo.”
My niece called her firstborn Chunk until he got past the baby fat stage.
My dad called me Juicy Fruit because I drooled so much. After I stopped drooling, he called me Boonie. I think it was from the song Down in The Boondocks.
One of my sisters was called Beanie because it rhymed with her name and the other sister was called Spider because she was really gangly as a baby (which morphed into Seppo because that’s how she pronounced Spider).
My grandma had names for all of her grandkids:
My Pet, Precious, Princess, Tiger, Creampuff, Boyfriend, Sugar Cookie, Banany, Peanut and Donut
I once overheard this phone conversation:
“Who’s this, Big Boo? Hey, Big Boo, lemme talk to Little Boo.”
Mmm
My first name is Jürgen, and my father had an acquaintance with the last name Jürgens and the nickname “Erbse”, which means “pea”. So my nickname for the first five or six years of my life became “Erbse”. Very rarely, my sister still calls me by that name to rile me up. 
ETA: does the inverse of the OP, a nickname given to you by a baby, also count? Because my oldest nephew as a baby couldn’t pronounce “Jürgen”, it sounded just like “Gugu” from his mouth, so the first few years of my nephew’s life my name in the family became Gugu.
Sure, why not? My granddaughter calls her step-grandfather (SIL’s stepdad) YaYa. No idea where that came from.
Ok, then I have a second example from my family: a great-uncle of mine was called Josef, which one of his nieces or nephews (can’t remember exactly who) pronounced “Sese” as a baby. This name stuck to him for the rest of his life in the whole family. We still call him Sese when we talk about him, more than 40 years after his death.
I’m sure he’s told that story to a number of therapists by now.
JK, but I hope someone has asked him if he likes it (providing you’re willing to stop if he doesn’t).
This hits a raw nerve because we have an in-law that we asked that question of, and he said he absolutely hated his nickname, and felt it was his family’s way of treating him like a child (and not taking anything he says seriously?).
But what I really hate is when a parent says “This is William. Now, we named him William, but he will NEVER be called Bill or Will.”
Ummm, why do you think that’s YOUR decision? And how are you going to enforce that twenty years from now?
He’s totally cool with it. We’ve talked about it while drinking beer, smoking weed, and micro-dosing shrooms.
Since any one of those counts as a lie detector test, my fears for Baby Bobby are allayed.
Not quite that strongly, but my inlaws are disappointed that my husband goes by an abbreviated version of his name, altho they use it themselves. The other two sons go by their given names which don’t lend themselves to nicknames.
My Mom did this exact thing. I’m ok with it though because I also despise the nickname version of my name.
Vaderling is Scoot, or Scooter. He scooted across the floor before he crawled or rolled as an infant. It’s starting to fade a little now as he enters the teen years, but I still think of him as Scoot in my head.
On the subject of names bestowed by children, the grandchild of a friend of mine, who we used to babysit together, called me Brendaddy (Bren being a variation of my RL name).
I did that with my Daughter, Amanda. Said to everyone, her name is Amanda, not Mandy. She’s now 30 and doesn’t answer to Mandy if someone call her that.
Before she was born, and we found out the sex, we called our first daughter “Cletus the Fetus.” With our second we called her “Barry.”
After the birth the nicknames haven’t been interesting enough for this thread.
When my sister was pregnant with her second, her daughter decided she wanted a brother named Freddy. She actually got a brother named Shawn, but she still called him Freddy.
When my son was born, my wife named him Firstname Middlename. I preferred Middlename Firstname, but gave in.
My daughter was three. I jokingly referred to her baby brother as Middlename Firstname a few times and she latched onto it as the truth.
She told people her baby brother’s name. They believed her. For awhile there was chaos.