WINAPIでMDI子ウィンドウが存在するのに表示されない

タイトルの通り、MDI子ウィンドウが存在しているのに、そのウィンドウが表示されません。
何がいけないのか調べてもわからなかったので、質問させていただきます。
ちなみにWM_SIZE部分をコメントアウトしたらしっかり表示されます。(描画がおかしくなりますが。)
ソースコード

C++
1#include <windows.h>
2#include <commctrl.h>
3
4#include "resource.h"
5#include "common.h"
6
7#pragma comment(lib,"comctl32.lib")
8
9#define TITLE TEXT("Hyper Map Editor")
10#define MDI_FRAME TEXT("FRAMEWINDOW")
11#define MDI_CHILD TEXT("MDICHILD")
12
13HINSTANCE hIns;//現在のインターフェース
14HWND hCHildWndMap;
15
16#define ID_CHILDWND 0x100
17LRESULT CALLBACK FrameProc(HWND hWnd, UINT msg, WPARAM wp, LPARAM lp) {
18	static HWND hToolbar;
19	static HBITMAP hBitmap;
20	CLIENTCREATESTRUCT ccsClient;
21	static HWND hClientWindow;
22	switch (msg)
23	{
24	case WM_DESTROY:
25		DeleteObject(hBitmap);
26		PostQuitMessage(0);
27		return 0;
28	case WM_CREATE:
29		ccsClient.hWindowMenu = GetSubMenu(GetMenu(hWnd), 4);
30		ccsClient.idFirstChild = ID_CHILDWND;
31
32		hClientWindow = CreateWindow(TEXT("MDICLIENT"), NULL,
33			WS_CHILD | WS_CLIPCHILDREN | WS_VISIBLE| WS_CLIPSIBLINGS,
34			0, 0, 0, 0, hWnd, (HMENU)1, ((LPCREATESTRUCT)lp)->hInstance, &ccsClient
35		);
36			InitCommonControls();
37			hBitmap = LoadBitmap(
38				((LPCREATESTRUCT)lp)->hInstance,
39				TEXT("IDB_BITMAP2")
40			);
41			hStatus = CreateWindowEx(
42				NULL,
43				STATUSCLASSNAME,
44				NULL,
45				WS_CHILD
46				| SBARS_SIZEGRIP
47				| CCS_BOTTOM
48				| WS_VISIBLE,
49				0, 0, 0, 0,
50				hWnd,
51				(HMENU)ID_STATUS,
52				((LPCREATESTRUCT)lp)->hInstance,
53				NULL
54			);
55
56			hToolbar = CreateToolbarEx(
57				hWnd,
58				WS_CHILD | WS_VISIBLE,
59				IDR_TOOLBAR1,
60				10,
61				NULL,
62				(UINT_PTR)hBitmap,
63				tbs,
64				18,
65				0, 0,
66				16, 16,
67				sizeof(TBBUTTON)
68			);
69		return 0;
70	case WM_SIZE:
71			SendMessage(hToolbar, WM_SIZE, wp, lp);
72
73			SbSize[0] = LOWORD(lp) - 400;
74			SbSize[1] = -1;
75			SendMessage(hStatus, SB_SETPARTS, 2, (LPARAM)SbSize);
76			//文字を挿入
77			SendMessage(hStatus, SB_SETTEXT, 0 | 0, (WPARAM)TEXT("MDI"));
78			SendMessage(hStatus, WM_SIZE, wp, lp);
79		return 0;
80	case WM_COMMAND:
81		switch (LOWORD(wp))
82		{
83		case IDM_NEWMINIMAP:
84			hCHildWndMap = CreateMDIWindow(MDI_CHILD, TITLE, 0,
85				10, 100,
86				50, 80,
87				hClientWindow, hIns, 0
88			);
89			break;
90		}
91		break;
92	}
93	return DefFrameProc(hWnd, hClientWindow, msg, wp, lp);
94}
95int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
96	PSTR lpCmdLine, int nCmdShow) {
97	HWND hWnd;
98	MSG msg;
99	WNDCLASS winc;
100	hIns = hInstance;
101
102	winc.style = CS_HREDRAW | CS_VREDRAW;
103	winc.lpfnWndProc = FrameProc;
104	winc.cbClsExtra = winc.cbWndExtra = 0;
105	winc.hInstance = hInstance;
106	winc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
107	winc.hCursor = LoadCursor(NULL, IDC_ARROW);
108	winc.hbrBackground = (HBRUSH)(COLOR_APPWORKSPACE + 1);
109	winc.lpszMenuName = TEXT("MYMENU");
110	winc.lpszClassName = MDI_FRAME;
111
112	if (!RegisterClass(&winc)) return 1;
113
114	winc.lpfnWndProc = DefMDIChildProc;
115	winc.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
116	winc.lpszClassName = MDI_CHILD;
117
118	if (!RegisterClass(&winc)) return 1;
119
120	hWnd = CreateWindow(
121		MDI_FRAME, TITLE,
122		WS_OVERLAPPEDWINDOW|WS_MAXIMIZE|WS_VISIBLE,
123		CW_USEDEFAULT, CW_USEDEFAULT,
124		CW_USEDEFAULT, CW_USEDEFAULT,
125		NULL, NULL, hInstance, NULL
126	);
127
128	if (hWnd == NULL) return 1;
129
130
131	while (GetMessage(&msg, NULL, 0, 0)) {
132		TranslateMessage(&msg);
133		DispatchMessage(&msg);
134	}
135
136	return msg.wParam;
137}