NO PRIMEIRO MODEL:

  @JsonProperty("tamanhos")
  @JsonDeserialize(as=ArrayList.class, contentAs=Sizes.class)
  private List<Sizes> sizes;

NO SEGUNDO MODEL, NO CONSTRUTOR:

@JsonCreator
  public Sizes(
      @JsonProperty("idtamanho") int id,
      @JsonProperty("nmtamanho") String nameSize,
      @JsonProperty("diametro") float size,
      @JsonProperty("qt_sabores") int countFlavors,
      @JsonProperty("qt_fatias") int countSlices,
      @JsonProperty("vl_pizza") float valuePizza) {
    this.id = id;
    this.nameSize = nameSize;
    this.size = size;
    this.countFlavors = countFlavors;
    this.countSlices = countSlices;
    this.valuePizza = valuePizza;
  }