[occultation]

Pitching Shadowfur and Alder as mentor/cool uncle figures for Flea

My thinking is that perhaps after running away, either due to fear or to look for their "parent" like you said, they unknowingly wander into a hostile rogue's territory. They witness this rogue fighting Shadowfur; the latter had been hunting this rogue down after witnessing him stealing prey from Shadow and Alder's territory.

Shadow ends up killing the rogue, spotting Flea soon after. Initially, Shadow thinks Flea is allied with this rogue, and is hostile as a result. Once that confusion is cleared up, he'd still be unwilling to help until he finds out that Flea is from ShadowClan. After that, Shadowfur invites the former apprentice to his and Alder's camp to rest for a while.

I don't know how much training Flea has had, but if he's lacking in combat training or you'd like him to learn some basic healing, Shadow and Alder can provide that. I imagine Flea would leave after a while, but Shadow and Alder would offer their help to him if he ever needs it in the future.

( @Batt. )