diff --git a/ui/children_count_test.go b/ui/children_count_test.go
new file mode 100644
index 00000000..4bee5b14
--- /dev/null
+++ b/ui/children_count_test.go
@@ -0,0 +1,56 @@
+//go:build !js || !wasm
+
+package ui_test
+
+import (
+	"testing"
+
+	"github.com/monstercameron/GoWebComponents/html"
+	"github.com/monstercameron/GoWebComponents/ui"
+)
+
+// Deepens the ReactChildren port toward equivalency for the GWC-applicable subset
+// (count / flatten / filter — GWC has html.Children normalization, not the
+// Children.map/forEach/count API). Mirrors React's count/flatten cases.
+func TestChildrenCountAcrossShapes(t *testing.T) {
+	span := func(parseS string) ui.Node { return html.Span(html.Props{}, ui.Text(parseS)) }
+
+	cases := []struct {
+		name string
+		in   []any
+		want int
+	}{
+		{"nil-only -> 0", []any{nil}, 0},
+		{"all-nil -> 0", []any{nil, nil}, 0},
+		{"empty -> 0", []any{}, 0},
+		{"single arrayless -> 1", []any{span("a")}, 1},
+		{"single in slice -> 1", []any{[]ui.Node{span("a")}}, 1},
+		{"flat -> 3", []any{span("a"), span("b"), span("c")}, 3},
+		{"nested 2 levels", []any{span("a"), []ui.Node{span("b"), span("c")}}, 3},
+		{"nested 3 levels", []any{[]any{[]ui.Node{span("a"), span("b")}, span("c")}}, 3},
+		{"mixed kinds", []any{"text", span("a"), []any{"more", span("b")}}, 4},
+		{"nil interspersed", []any{span("a"), nil, span("b"), nil, span("c")}, 3},
+	}
+	for _, parseCase := range cases {
+		if parseGot := len(html.Children(parseCase.in...)); parseGot != parseCase.want {
+			t.Errorf("%s: count = %d, want %d", parseCase.name, parseGot, parseCase.want)
+		}
+	}
+}
+
+// Deeply nested children flatten in document order (a mis-ordered or partial
+// flatten would scramble the rendered output).
+func TestChildrenDeepFlattenOrder(t *testing.T) {
+	parseNodes := html.Children(
+		ui.Text("1"),
+		[]any{ui.Text("2"), []ui.Node{ui.Text("3"), ui.Text("4")}},
+		ui.Text("5"),
+	)
+	parseOut, parseErr := ui.RenderToString(html.Div(html.Props{}, parseNodes...))
+	if parseErr != nil {
+		t.Fatalf("render error: %v", parseErr)
+	}
+	if parseOut != "<div>12345</div>" {
+		t.Errorf("deep flatten order = %q, want <div>12345</div>", parseOut)
+	}
+}