Maven plugin inheritance from pluginManagement - maven

Question

there
I have a parent pom.xml which defines the the default configuration for maven-ear-plugin
<pluginManagement>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-ear-plugin</artifactId>
<version>2.8</version>
<configuration>
<modules>
<jarModule>
<groupId>com.test</groupId>
<artifactId>artifact1</artifactId>
</jarModule>
<jarModule>
<groupId>com.test</groupId>
<artifactId>artifact2</artifactId>
</jarModule>
</modules>
</configuration>
</plugin>
</plugins>
</pluginManagement>
In the child pom, I defined the maven-ear-plugin in the <plugins> section
<plugin>
<artifactId>maven-ear-plugin</artifactId>
<executions>
<execution>
<id>default-ear</id>
<phase>package</phase>
<goals>
<goal>ear</goal>
</goals>
<configuration>
<earSourceDirectory>EarContent</earSourceDirectory>
<defaultLibBundleDir>APP-INF/lib</defaultLibBundleDir>
<modules>
<jarModule>
<groupId>com.test</groupId>
<artifactId>artifact3</artifactId>
</jarModule>
</modules>
</configuration>
</execution>
</executions>
</plugin>
My intention is to include all 3 jar files artifact1, artifact2 and artifact3 in the ear. However, after the build, only artifact3 defined in child pom.xml is included. So it looks like by default the <modules> definition in the child pom.xml overwrites what's defined in the parent pom, instead of merge them together. In fact, if I remove the whole <modules> section in the child pom.xml, the artifact1 and artifact2 will be included after the build.
My question is whether there is a way to include all jar modules defined in parent pom and child pom. I have several ear projects and all of them need to include the same set of jar modules plus a few jar modules of their own. I am trying to move the common set of jar modules to the parent so that they are not repeated in each child pom.xml.
Update to clarify my projects relations:
parent pom.xml (define maven-ear-plugin in the pluginManagement section)
-- project1 pom.xml (multi-module project)
-- myJar-proj1
-- myWeb-proj1
-- myEar-proj1 (define maven-ear-plugin in the <build> section)
-- project2 pom.xml (multi-module project)
-- myJar-proj2
-- myWeb-proj2
-- myEar-proj2 (define maven-ear-plugin in the <build> section)

Answer 1

In order to achieve the merge behavior you should put the maven-ear-plugin under the plugins tag in the parent pom (rather than under pluginManagement).
Parent pom:
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-ear-plugin</artifactId>
<version>2.8</version>
<configuration>
<modules>
<jarModule>
<groupId>com.test</groupId>
<artifactId>artifact1</artifactId>
</jarModule>
<jarModule>
<groupId>com.test</groupId>
<artifactId>artifact2</artifactId>
</jarModule>
</modules>
</configuration>
</plugin>
</plugins>
</build>
EDIT
After OP's clarified projects structure: the attribute combine.children="append" on the modules element, in the child projects:
<modules combine.children="append">
<jarModule>
<groupId>com.test</groupId>
<artifactId>artifact3</artifactId>
</jarModule>
</modules>
The parent should still define the plugin only in pluginManagement.