How to find all control inside a div?

I have two div control in my aspx page. Inside first div contrl i have five textbox and one button and in secord div i have four text box and two button. 
Now i want to find all controls inside div by using getElementsByTagName in javascript?
<div> <asp:TextBox ID="TextBox3" runat="server"></asp:TextBox><br /> <asp:TextBox ID="TextBox4" runat="server"></asp:TextBox><br /> <asp:TextBox ID="TextBox5" runat="server"></asp:TextBox><br /> <asp:TextBox ID="TextBox6" runat="server"></asp:TextBox><br /> <asp:TextBox ID="TextBox7" runat="server"></asp:TextBox><br /> <asp:TextBox ID="TextBox8" runat="server"></asp:TextBox><br /> <asp:Button ID=" ...