Sprout
Sproutling
Nick
Nicklebug
Nicklebean
Little Bean
Bean
Bug
Little Bug
Poopy Boy
Squishy
Squishy cheeked boy
Squishy baby
St. Bernard Boy
Drooly boy
Squirmy boy
Pukey boy
BOB
Sucky boy
little boob baby
boo
booby boy
frog boy
smallish boy (this one the most, recently)
smallish
nickelsprout
mullet boy (not any more)
bebe
milky boy
the boy

and probably more...

eta: sweet baby
minty (fresh) boy/baby
peanut
peanut butter
kicky boy/baby
blue eyes
big eyed baby

eta:
peach head
skishy
stuntbutt