How can I include resources (css, js) from jar using maven assembly?

I have a project which contains shared resources for several sub-projects; i.e. as well as Java code, it contains css and javascript.

My child sub-projects are packaged as jars using the maven assembly plugin. For some reason these do not include the css and js resources from the parent library.

So my question is simple: how can I configure the projects so that this happens? I don't want the child projects to be wars; they are dropwizard (/jetty) projects that run as standalone jars.

EDIT - I should make explicit that the resources are included in the parent project's jar; it's only when assembly (on a child project) includes the jar that they somehow go missing.

Parent pom:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation=
                "http://maven.apache.org/POM/4.0.0 
                 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>io.parentproject</groupId>
    <artifactId>parentproject</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        ...
    </dependencies>

    <build>
        <resources>
            <resource>
                <directory>src/main/webapp</directory>
            </resource>
            <resource>
                <directory>src/main/resources</directory>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.java</include>
                    <include>**/*.gwt.xml</include>
                </includes>
            </resource>
        </resources>
        <plugins>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <compilerArgument>-proc:none</compilerArgument>
                    <fork>true</fork>
                </configuration>               
            </plugin>
            <plugin>
                <artifactId>maven-jar-plugin</artifactId>
                <version>2.3.2</version>
                <configuration>
                    <archive>
                        <manifest>
                            <addDefaultImplementationEntries>
                                true
                            </addDefaultImplementationEntries>
                        </manifest>
                    </archive>
                </configuration>
            </plugin>
            ...
        </plugins>
    </build>
</project>

Example child pom:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" 
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation=
                "http://maven.apache.org/POM/4.0.0 
                 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>io.child</groupId>
    <artifactId>child</artifactId>
    <version>1.0-SNAPSHOT</version>

    <name>Child</name>

    <dependencies>
        <dependency>
            <groupId>io.parentproject</groupId>
            <artifactId>parentproject</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
        ...
    </dependencies>

    <build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
            </resource>
            <resource>
                <directory>src/main/webapp</directory>
            </resource>
        </resources>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <compilerArgument>-proc:none</compilerArgument>
                    <fork>true</fork>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
                <version>2.3.2</version>
                <configuration>
                    <archive>
                        <manifest>
                            <addDefaultImplementationEntries>
                                true
                            </addDefaultImplementationEntries>
                        </manifest>
                    </archive>
                </configuration>
            </plugin>            
            <plugin>
                <artifactId>maven-assembly-plugin</artifactId>
                <version>2.4</version>
                <configuration>
                    <descriptorRefs>
                        <descriptorRef>jar-with-dependencies</descriptorRef>
                    </descriptorRefs>
                    <archive>
                        <manifest>
                            <mainClass>io.childproject.SomeClass</mainClass>
                        </manifest>
                    </archive>
                    <finalName>${project.artifactId}-${project.version}</finalName>
                    <appendAssemblyId>false</appendAssemblyId>
                </configuration>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>assembly</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
             ...
        </plugins>
    </build>

</project>