Well, Littlefoot has a problem: The only female Longneck that we know of in the Great Valley is Grandma Longneck!!!!!
There seem to be the following Longnecks in the Great Valley that we know of:
Males: Littlefoot (Kid), Grandpa Longneck (Grandfather and already married), Pat (kinda old)
Females: Grandma Longneck (Grandmother and already married)
Maybe Bron and Shorty will come there after the end of 14, but that still won't help Littlefoot find a wife!
Indeed, the only female Littlefoot's age that we know of is Ali, and there is now a problem with that that the TV Series introduced:

Rhett may be a creep, but Ali will likely be spending a lot more time with him than Littlefoot over the years, so Littlefoot will have to find some way to impress Ali to get her to choose him over her friend that she spends more time with.
Unless a Longneck herd comes to the Great Valley to stay, Littlefoot is going to have to look outside the Great Valley for a mate and so he may have a painful choice too, especially if she turns out to be someone other than Ali, who might not like living in the Combined Herd, and he may have to forgo his friends as well or at least maybe live outside the Great Valley.
Also, even Ali might not be so tolerant of other kinds. I know she improved in IV, but she probably still has some to learn still.
I mean, I can see it now if Littlefoot goes outside the Great Valley looking for a mate.
Littlefoot: So I'm friends with a Threehorn, a Swimmer, a Flyer, a Spiketail, a Sharptooth, and a Fast Runner.
Other Longnecks:

Loser!
Littlefoot:
