Littlefoot, Chomper, and Spike appear to be only children.
I mean, Cera has siblings (where they went, we don't know) and she now has Tricia. Petrie and Ducky have them too.
Also, oddly enough, it appears that Littlefoot's mother may have been an only child too as Littlefoot appears to have no aunts or uncles. (Which may mean Bron was an only child too. Perhaps longneck egg mortality is high.)
Also, Petrie's mom isn't an only child as Pterano is her brother.
Grandpa and Grandma Longneck and Topps are old enough that we cannot infer if they are only children or not.
Ali also appears to be an only child. Whether Rhett and Shorty are or whether their siblings were eaten or died some other way is unknown.
(Note, Littlefoot is counted an only child because his sibling eggs were all destroyed by the time he hatched and hence he never met them or could have met them.)
One of Ducky's parents can't be an only child as Ducky has an aunt.
Guido may or may not be. (Perhaps he suffered some tragedy that cost him his family and he got memory impairment or something from the incident.)
Also, Ozzy and Strut are brothers. They can't be only children. (Ozzy and Strut might wish they were, but they aren't.)
Ruby has siblings. She's not an only child.
