Json conversion with GSON: Expected BEGIN_ARRAY but was BEGIN_OBJECT

for learning purpose I want to build a simple android REST client using retrofit and Gson. This is my Json string I want to parse:

{
  "kind": "Listing",
  "data": {
    "modhash": "qo2fwmjj5iee4adde638f97d5a7063087439bf4985aab4c9a5",
    "children": [
      {
        "kind": "t5",
        "data": {
          "banner_img": "",....

My data model:

public class Response {

    @SerializedName("kind")
    private String kind;

    @SerializedName("data")
    private Data data;

    public String getKind() {
        return kind;
    }

    public void setKind(String kind) {
        this.kind = kind;
    }


    public Data getData() {
        return data;
    }

    public void setData(Data data) {
        this.data = data;
    }
}

public class Data {

    @SerializedName("modhash")
    private String modhash;

    @SerializedName("after")
    private String after;

    @SerializedName("before")
    private String before;

    @SerializedName("children")
    private List<Child> children;

    public String getModhash() {
        return modhash;
    }

    public void setModhash(String modhash) {
        this.modhash = modhash;
    }

    public String getAfter() {
        return after;
    }

    public void setAfter(String after) {
        this.after = after;
    }

    public String getBefore() {
        return before;
    }

    public void setBefore(String before) {
        this.before = before;
    }

    public List<Child> getChildren() {
        return children;
    }

    public void setChildren(List<Child> children) {
        this.children = children;
    }
}

public class Child {
    @SerializedName("kind")
    private String kind;
    @SerializedName("data")
    private List<Sub> data;

    public String getKind() {
        return kind;
    }

    public void setKind(String kind) {
        this.kind = kind;
    }

    public List<Sub> getData() {
        return data;
    }

    public void setData(List<Sub> data) {
        this.data = data;
    }
}

Unit Test:

public class Test {

    private GsonConverter gsonConverter;
    private  Gson gson;

    private Logger logger = Logger.getLogger(Test.class.getName());

    public  Test() {
         gson = new GsonBuilder()
                .setDateFormat("yyyy'-'MM'-'dd'T'HH':'mm':'ss'.'SSS'Z'")
                .create();
        gsonConverter = new GsonConverter(gson);
    }

    @Test
    public void testData() {
        Response response = gson.fromJson(TestUtil.RESPONSE_STRING, Response.class);
        logger.info("Data " + response.getData());

        Assert.assertNotNull(response.getData());
    }
}

So when the parser reaches the "children" attribute, following error occurs.

Caused by: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was BEGIN_OBJECT
    at com.google.gson.internal.bind.JsonTreeReader.expect(JsonTreeReader.java:139)
    at com.google.gson.internal.bind.JsonTreeReader.beginArray(JsonTreeReader.java:58)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:79)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read

Don't know what to do, tried different things, do I have to handle the "children" by myself because of the [ bracket?