The interpretation of Cera's jealousy could go either way but I lean toward platonic. I'm under the impression Cera sometimes sees getting a new friend means replacing a old one while Littlefoot and the others see a new friend as a addition that widens the circle. However she complains, she dearly values her bond with the gang and doesn't want it to be endangered. Once she realizes the likes of Ali and Mo are additions to the group rather than replacing anyone, she cools and warms up to these new bonds.
Of course, Cera crushing on Littlefoot can be possible, in the canon or at any future point in their lives. Elsie thought Grandpa Longneck was quite fetching, so crushes between species is a thing, even if she resigns their different types means nothing would come from it (Though strangely, she either doesn't know or isn't concerned he already having a mate means nothing would come from it.). Though in a wide world as big as theirs, the chances are there were a few dinosaurs of different types who tried to couple up and the gang have been shattering social mores since their friendship began. Not saying those social mores wouldn't give them pause, but I wouldn't be surprised if a few of their generation, who are used to mixed-species friendships, wouldn't at least be curious enough to experiment with a mixed-species romance.
So if Cera and Littlefoot do have crushes on each other, they might try it out. There will be struggles. The dating process in the ideal is already complicated enough, with figuring out if you enjoy being together, can get along, and what exactly this romance thing entails. Any prejudices they might deal with might add further wrenches, since they might stick together out of stubbornness and stifle conflicts or arguments to show their bond can work. This can be a problem, since learning how to navigate conflicts and arguments and settle them in a healthy manner is part of the dating process and Cera and Littlefoot would especially need to learn that. And there's the fact that sometimes oops, this isn't who they want to spend the rest of their life with after all or the flame goes out, and the pair would have to figure out what their bond, if any, would be from there. This is especially the case for teenage relationships. Not saying it couldn't work out, if they can work out the conflicts of their friendship, they might do so as a couple and it might be what they want after all, screw social mores. But there will be complications.
As for having children - I don't think they would be able to do so but a) not all couples want children, even if they might get along with them and b) they could adopt if the opportunity strikes.
Though if it is successful and/or if others do the same, I can picture some outside communities tutting disapprovingly, thinking the Great Valley has become more of a "free love interspecies mixing hippie commune" than they already believe it is (Yes, I know "hippie" and "commune" are probably not in their vocabulary, but I couldn't think of their equivalent for those words, so there you go).
