I believe there is definitely something between them; a sibling relationship. For one thing, they've known each other the longest, meaning they would be closer to each other than anyone else. Littlefoot seems to be Cera's protector. He shows the most concern if something's troubling her, is always available to listen to her (making him her confidant), and pays special attention to her safety in times of danger. She seems to return the favor to him. One example was in LBT 12, when Littlefoot was struggling to pull himself up over the cliff. Even though Ducky tried to help him but is so small (bless her heart for caring so much), Cera is the only reasonably sized one to help him up. I've also noticed Cera plays the part of Littlefoot's advisor, helping him with leadership decisions. Another thing I saw was in LBT 13, when the gangs were singing "How Do You Know?" (sorry 'bout the spoiler, fellow European members :^.^:), Littlefoot appears to rest his cheek on Cera's forehead at the close of the song. Before I ramble on any further, I believe these two love each other, look out for each other and always will share the bond they do :^.^: :^.^:.
(Stops to catch breath) Phew! That's a rap, y'all.