In your example you have not used the input-prepend class in the second input , you should write it as follows
<div class="cell input-prepend">
<input type="number"/>
</div>
And in css remove width=100% from input and use margin-right
input[type=text] {
margin-right:10px;
}
Can you please check the JSfidlle updated JSfiddle prepend
<div class="container">
<div class="row">
<form class="form-inline">
<input type="text" class="input-small" placeholder="Email">
<input type="password" class="input-small" placeholder="Password">
</form>
<form class="form-inline">
<input type="text" class="input-small" placeholder="Email">
<input type="password" class="input-small" placeholder="Password">
</form>
</div>
</div>