I could see hades trying to coax Pais to trust him, maybe at first with little words and compliments, maybe Pais only thinks hades is a shadow that talks to him. Pais wouldn't know, he's not told anything and it kinda sounds like something the younger gods told him about. He's never been told of the previous guardian, so the shadow must have been shy and lived around here for a while if he knows so much, like where the creek is and the hand holds best to climb the tree. Why would they tell him of his predecessor if they don't want him getting any ideas about being like hades? Maybe the shadow ends up being the one Pais talks about his feelings too, not the younger gods (what if they would never come back if they aren't having fun?) Or the elder ones (nagging, always nagging, never happy with a single thing Pais does, never enough, always lecturing) Hades eventually even telling a story or two sometimes, just to get the little god to sleep so he can slink away.
Maybe hades remembers a time when he too, was alone night after night at the tree. How his solace was the stories he could read. How Pais is denied even that. Telling Pais stories of the outside at first, just to make the little god wonder. Then of the underworld as well, and occasionally one of the valued texts hades hoards.
His four mortal soul minions wondering why it is their patron God is looking at scrolls to do with children. Getting confused at a question hades may pose to them about mortal children even. If hades can send them out to wander and do his bidding, they could collect things to entice Pais with. (And also pick up a scroll or two, that won't ever be turned down by hades)
Oh yes, Hades will certainly try to coax little Pais into trusting him. Praise will be too sweet for a boy who hardly recieves any to resist. Hades' shadow form will also work in his favor- not too intimidating, yet mysterious enough to peek his curiosity.
And you're right of course, Hades has more than enough tales to tell, especially of earth, to make the little godling wonder . . . .
. . . and hopefully, eventually, wander.