I think one thing it's important to note is the difference between Halsin's ordeal with leadership at the Grove and the role he takes at the commune at the end.
When he is forced to take over at the Grove, it's just that: something forced on him, and while he's dealing with the trauma from losing his mentor, whose position he is forced to take over. No one helped prepare him for the role, and he doesn't seem to be getting help once in it either. He repeatedly refers to this as an isolating experience, with his peers "replaced by the weight of responsibility." He loses a sense of community by being forced to lead, and further, he fears (during act 3) that the time he spent in the position cost him his chance to start his own family. It's also important to note that Druids practice a fairly authoritative style of leadership; this is shown more in previous DND editions, but we get glimpses of it here too.
While we don't see as much of his leadership at the commune, Halsin alludes several times to it being a mutual effort. He mentions others giving input as well, and there being friction (such as due to different personalities and cultures) that they work through together. Which means conflict resolution doesn't fall solely on him (another sore point he cited at the Grove). He mentions feeling a greater sense of balance. And yes, the children are important to him as well because he gains family and community here, instead of feeling like he can only be a leader; he clearly feels this group are much more like peers he can mutually rely on, if sometimes guiding, as opposed to the Grove where he wasn't allowed to be vulnerable. Here, he's practicing the leadership that's more in the sense of being a trusted and respected elder than being the sole authority. Those two are very distinct, and the difference is clearly what makes one something that made Halsin miserable, and the other something that brings him healing.
In fact, you can even get hints of this before the epilogue; when he laments that he feels he failed the Grove after getting Francesca's letter, you can tell him it's okay to not be cut out for leadership, which he agrees with, but laments that he wants to pass on all the knowledge he's gained in his life on to someone. The Druids at his Grove weren't open to it (for whatever reason), whereas those at the commune actually want to hear it.
I know it sounds odd that after hating leading the Grove so much and learning that he's allowed to exist without a purpose, his happy ending involves him being a leader again, but the difference between a leader as in an authority and a leader as in a trusted elder is the crucial difference, I think. He's not "Master Halsin" here, he's "Daddy Halsin," the wise old bear who gets to play with the little ones and give input to people who are wounded but healing like himself. He may lead them, but he's still their equal- their friend and family.
