Elliot is actually Pete's deceased dad come back as his guardian angel.
- Then the "other kid" could be another child of his. Or he realized now that Pete has a new family, he won't need him anymore and goes off to help other kids. It makes their good-bye that much more heartbreaking.
The next sequel (should it ever comes) will take place in the Present Day with another kid he's helping.
- More or less; no sequel planned, but a reboot that may be a sequel at the same time, see next entry.
The 2016 "remake" is in fact a sequelIt is just a coincidence that Elliott gets to help another kid named Pete.
Pete is a Targaryen.