您必须对父节点进行排序，并创建包含每个父节点和下一个父节点的元组。然后，对于每个范围，您必须找到此范围内的所有付款（running example）：

var parents = new[]
{
    new DateOnly(2023, 4, 26),
    new DateOnly(2023, 4, 28),
    new DateOnly(2023, 4, 18),
};

var childs = new[]
{
    new DateOnly(2023, 4, 22),
    new DateOnly(2023, 4, 25),
    new DateOnly(2023, 4, 27),
    new DateOnly(2023, 4, 17),
    new DateOnly(2023, 4, 21),
};

var parentsOrdered = parents.OrderDescending().Append(DateOnly.MinValue);
var payments = parentsOrdered
    .Zip(parentsOrdered.Skip(1), (batch, limit) => (batch, limit))
    .Select(range => (range.batch, childs: childs.Where(child => range.limit < child && child < range.batch)));

foreach (var payment in payments)
{
    Console.WriteLine($"Batch: {payment.batch}");
    foreach (var child in payment.childs)
    {
        Console.WriteLine($"   {child}");
    }
}