diff --git a/core/src/test/java/org/elasticsearch/search/aggregations/AggregationsTests.java b/core/src/test/java/org/elasticsearch/search/aggregations/AggregationsTests.java
index a70c3c2d1b4..48fa42ad3ef 100644
--- a/core/src/test/java/org/elasticsearch/search/aggregations/AggregationsTests.java
+++ b/core/src/test/java/org/elasticsearch/search/aggregations/AggregationsTests.java
@@ -115,8 +115,6 @@ public class AggregationsTests extends ESTestCase {
         aggsTests.add(new InternalMissingTests());
         aggsTests.add(new InternalNestedTests());
         aggsTests.add(new InternalReverseNestedTests());
-        // TODO can we find a way to include the children aggregation in this test?
-        //aggsTests.add(new InternalChildrenTests());
         aggsTests.add(new InternalGlobalTests());
         aggsTests.add(new InternalFilterTests());
         aggsTests.add(new InternalSamplerTests());
@@ -129,7 +127,7 @@ public class AggregationsTests extends ESTestCase {
 
     @Override
     protected NamedXContentRegistry xContentRegistry() {
-        return new NamedXContentRegistry(InternalAggregationTestCase.getNamedXContents());
+        return new NamedXContentRegistry(InternalAggregationTestCase.getDefaultNamedXContents());
     }
 
     @Before
@@ -147,9 +145,9 @@ public class AggregationsTests extends ESTestCase {
     }
 
     public void testAllAggsAreBeingTested() {
-        assertEquals(InternalAggregationTestCase.getNamedXContents().size(), aggsTests.size());
+        assertEquals(InternalAggregationTestCase.getDefaultNamedXContents().size(), aggsTests.size());
         Set<String> aggs = aggsTests.stream().map((testCase) -> testCase.createTestInstance().getType()).collect(Collectors.toSet());
-        for (NamedXContentRegistry.Entry entry : InternalAggregationTestCase.getNamedXContents()) {
+        for (NamedXContentRegistry.Entry entry : InternalAggregationTestCase.getDefaultNamedXContents()) {
             assertTrue(aggs.contains(entry.name.getPreferredName()));
         }
     }
diff --git a/modules/parent-join/src/test/java/org/elasticsearch/join/aggregations/InternalChildrenTests.java b/modules/parent-join/src/test/java/org/elasticsearch/join/aggregations/InternalChildrenTests.java
index 089f0a19bd9..95cff14ef00 100644
--- a/modules/parent-join/src/test/java/org/elasticsearch/join/aggregations/InternalChildrenTests.java
+++ b/modules/parent-join/src/test/java/org/elasticsearch/join/aggregations/InternalChildrenTests.java
@@ -22,22 +22,25 @@ package org.elasticsearch.join.aggregations;
 import org.elasticsearch.common.ParseField;
 import org.elasticsearch.common.io.stream.Writeable.Reader;
 import org.elasticsearch.common.xcontent.NamedXContentRegistry;
+import org.elasticsearch.common.xcontent.NamedXContentRegistry.Entry;
 import org.elasticsearch.search.aggregations.Aggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.InternalSingleBucketAggregationTestCase;
 import org.elasticsearch.search.aggregations.bucket.ParsedSingleBucketAggregation;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
-import org.junit.BeforeClass;
 
+import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 
 public class InternalChildrenTests extends InternalSingleBucketAggregationTestCase<InternalChildren> {
 
-    @BeforeClass
-    public static void init() {
-        namedXContents.add(new NamedXContentRegistry.Entry(Aggregation.class, new ParseField(ChildrenAggregationBuilder.NAME),
+    @Override
+    protected List<NamedXContentRegistry.Entry> getNamedXContents() {
+        List<Entry> extendedNamedXContents = new ArrayList<>(super.getNamedXContents());
+        extendedNamedXContents.add(new NamedXContentRegistry.Entry(Aggregation.class, new ParseField(ChildrenAggregationBuilder.NAME),
                 (p, c) -> ParsedChildren.fromXContent(p, (String) c)));
+        return extendedNamedXContents ;
     }
 
     @Override
diff --git a/test/framework/src/main/java/org/elasticsearch/test/InternalAggregationTestCase.java b/test/framework/src/main/java/org/elasticsearch/test/InternalAggregationTestCase.java
index d85f41fd20c..bd084bd5c08 100644
--- a/test/framework/src/main/java/org/elasticsearch/test/InternalAggregationTestCase.java
+++ b/test/framework/src/main/java/org/elasticsearch/test/InternalAggregationTestCase.java
@@ -130,7 +130,8 @@ public abstract class InternalAggregationTestCase<T extends InternalAggregation>
             new SearchModule(Settings.EMPTY, false, emptyList()).getNamedWriteables());
 
     private final NamedXContentRegistry namedXContentRegistry = new NamedXContentRegistry(getNamedXContents());
-    protected static final List<NamedXContentRegistry.Entry> namedXContents;
+
+    private static final List<NamedXContentRegistry.Entry> namedXContents;
     static {
         Map<String, ContextParser<Object, ? extends Aggregation>> map = new HashMap<>();
         map.put(CardinalityAggregationBuilder.NAME, (p, c) -> ParsedCardinality.fromXContent(p, (String) c));
@@ -175,7 +176,11 @@ public abstract class InternalAggregationTestCase<T extends InternalAggregation>
                 .collect(Collectors.toList());
     }
 
-    public static List<NamedXContentRegistry.Entry> getNamedXContents() {
+    public static List<NamedXContentRegistry.Entry> getDefaultNamedXContents() {
+        return namedXContents;
+    }
+
+    protected List<NamedXContentRegistry.Entry> getNamedXContents() {
         return namedXContents;
     }