I’ve been pondering this theory all day and I think there are a few distinct possibilities.
-It’s Rumple’s toy from his stint as a lost boy on the island (no relation to Pan)
-Pan and Rumple are siblings (or related somehow) and Rumple may or may not have been a Lost Boy at some point
-The doll belongs to someone else entirely that is related somehow to Rumple (and who he cares very much about)
I can’t say which one I’m going to give credence to- but I definitely think we’re going to see the Stiltskin family tree expand for a few reasons.
-Neal’s lines about how important family is to Rumple, coupled with the introduction of “blood magic” makes it seem like we’re going to see more of both in the near future. This definitely sounds like a setup where someone who was not previously known to be related is going to pick up an item and it will cause the magic to react.
-Sometimes, lines are set up with false information so they can be proven wrong in a surprising way later, so while this may be fishing for something that isn’t there, I found it strange that they specified Neal was Rumple’s “only” son. Why not just say “son”? It’s not incorrect, by a long shot, but it seemed suspicious in way that might me we’d find out he isn’t. Maybe a firstborn son met an untimely fate when Rumple was unable to do anything about it? And that’s why he was so ready to do whatever it took to ensure Bael’s wellbeing? Robin’s stated that nobody would claim to be Rumple’s son unless they were also made me raise an eyebrow.
That being said, I hadn’t even considered the possibility that Pan and Rumple were brothers. If that toy did in fact belong to them once upon a time (sure, why not- it looks like it’s made out of corn husks, but we can pretend it’s straw) I can definitely see a scene play out where the toy was taken from big brother Peter and given to little Rumple because Peter was “too old” for toys- triggering his desire for eternal youth.
However, it would be strange for parents to have children named “Rumplestiltskin” (that time period/land lends itself to some exotic names) and “Peter”. The accents (super British and super Scottish) also don’t match at all. But it Rumple was raised by Spinsters, who is to say he didn’t have an adopted brother or sister? If the two were raised as brothers, and end up resolving this conflict peacefully, perhaps it would be an opportunity for the show to mend some of the “blood relations trump adoptive family” issues people have found problematic.
"Nothing is easier than to denounce the evildoer; nothing is more difficult than to understand him."