private com.google.protobuf.SingleFieldBuilderV3<
            com.google.protobuf.Int32Value,
            com.google.protobuf.Int32Value.Builder,
            com.google.protobuf.Int32ValueOrBuilder>
        getChildSpanCountFieldBuilder() {
      if (childSpanCountBuilder_ == null) {
        childSpanCountBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.protobuf.Int32Value,
                com.google.protobuf.Int32Value.Builder,
                com.google.protobuf.Int32ValueOrBuilder>(
                getChildSpanCount(), getParentForChildren(), isClean());
        childSpanCount_ = null;
      }
      return childSpanCountBuilder_;
    }
<pre>
Optional. The number of child spans that were generated while this span
was active. If set, allows implementation to detect missing child spans.
</pre>

<code>
.google.protobuf.Int32Value child_span_count = 13 [(.google.api.field_behavior) = OPTIONAL];
</code>
java-trace/proto-google-cloud-trace-v2/src/main/java/com/google/devtools/cloudtrace/v2/Span.java