<!-- First way -->
<input type="button" value="This is&#x00A;a Really&#x00A;Tall&#x00A; Button">
<!-- Second way -->
<button>This is<br/>a Really<br/>Tall<br/>Button</button>

http://www.apphp.com/index.php?snippet=html-button-with-line-breaks

To get button with line breaks you can use carriage return characters to break the line: &#x00A; or just <br> with a <button> tag:

Button With Line Breaks in HTML

button, line

HTML