public async Task <ChildOrder[]> GetChildOrders(ProductCode productCode,
                                                        int?count = null, int?before = null, int?after = null)
        {
            var query = new Dictionary <string, object>
            {
                { "product_code", productCode.GetEnumMemberValue() }
            };

            if (count != null)
            {
                query["count"] = count.Value;
            }
            if (before != null)
            {
                query["before"] = before.Value;
            }
            if (after != null)
            {
                query["after"] = after.Value;
            }

            return(await Get <ChildOrder[]>(GetChildOrdersApiPath, query));
        }