trees - AdjacencyList of DirectedEdges in Graph ignore edge direction

I have a simple tree graph with directed edges:

In: AdjacencyList[Graph[{a -> b, a -> c, b -> d, b -> e}], b]
Out: {a, d, e}

I wonder how I can select only the outgoing edge vertices elegantly.

{d, e}

In other words: I want the children of a vertex only.

The obvious solution for a tree is to always drop the first vertex. Sadly this approach fails for the root vertex, so there has to be some If-branching - which I want to avoid.

So far I tried VertexOutComponent and IncidenceList but non of them seems to give the option to filter by edge direction.

Do you see an elegant approach there, or will I have to keep using root checks?

Answer

VertexOutComponent gives

VertexOutComponent[g, b, 1]
(* {b, d, e} *)

This is precisely what you are looking for, plus the vertex b itself.

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To retrieve the full adjacency list of a directed graph, you can also use IGAdjacencyList from IGraph/M.

g = Graph[{a -> b, a -> c, b -> d, b -> e}];

IGAdjacencyList[g, "Out"]
(* <|a -> {b, c}, b -> {d, e}, c -> {}, d -> {}, e -> {}|> *)

IGAdjacencyList[g, "In"]

(* <|a -> {}, b -> {a}, c -> {a}, d -> {b}, e -> {b}|> *)