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Here are a few:
1) Koosy (adj.): This one started on my dad's side - the Geertsmas, a family of 12 - and continues to be widely used by almost all of the ten kids (my aunts and uncles) and their kids (my 40+ cousins on that side). It has even spread to my mom's side of the family. My dad and his sibs are first-generation Americans, and supposedly "koosy" is from a Fries word. It means small, chubby, fuzzy, irresistable, so cute you can't stand it any more, or all of the above.
2) Koos (verb): You can also "koos" someone, meaning you smash your face and lips onto someone's cheeks, non-existent/copious neck, or fuzzy head. For me koosing also involves nibbling on said cheeks and taking a good whiff of koosy-baby scent while I'm at it. Mona gets koosed around here too, in which case we almost suffocate in her fuzzy neck folds. (Obsessed? Yes.)
3) Koosbomb (noun): Someone who is explosively koosy.
4) Boopus: This one came from my mom's dad, Grandpa Dieken. A boopus is a round baby tummy that extends well beyond the waistline.
5) Brutus: A mad baby. (From my dad).
6) Chunky Tuna: My dad used to call Tyler this name as a toddler. A Chunky Tuna is an unusually short, stocky child.
7) One-ton-son: My dad again. (He is prolific with the terminology.) This one means a rather substantial boy baby. Hopefully this isn't culturally inappropriate, but we say it with choppy, forceful syllables that make it sound like a karate move. We joke that it's Jude's "Asian name". (Okay, that's definitely culturally inappropriate.)
8) Fat Bracelet: I think this one originated with me, but I can't be sure. When a roll of chub forms on a baby's wrist, it's obviously a fat bracelet.
9) Pooker-snook: From my mom. It pops out of her mouth whenever she sees Jude, and I think she called Grant a pooker-snook for awhile too. It's just something she calls a baby she likes a lot.
10) Bunners: A baby's butt. I think this one is from my Aunt Marian.
11) Package: It's not what you think. A package is a small, compact baby, usually when dressed in a sleep sack that makes him/her look like "a sack of potatoes" (there's another term right there).
12) Diaper Butt: A butt that is significantly enlarged by the presence of a bulky diaper.
I'm sure there are more, and if you think of any to add to my list, send them please.
(No Aunt Bonita, I'm not going to add "reg" or "reeg" or whatever to this list. It's obscene ;)
Additions:
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Needs Johnson - a whiner.
Twinkle Toes - when a baby haltingly walks on his or her tip-toes.
(Dictionary pic from woodywoodcutter.wordpress.com)