Илья

<div id="parent">
  <div class="first">
    <input value="25" type="checkbox" checked>
    <input value="50" type="checkbox" checked>
    <input value="100" type="checkbox">
    <input value="150" type="checkbox">
  </div>
  <div class="second">
    <input value="25" type="checkbox">
    <input value="50" type="checkbox">
    <input value="100" type="checkbox" checked>
    <input value="150" type="checkbox" checked>
  </div>
</div>

var list = {};
$('#parent>div').each(function(ii,div){
	list[$(div).attr('class')] = $.map($(div).find('input'),function(el){
  	if($(el).is(':checked')) return parseInt($(el).val());
  });
});
console.log(list);

{
  first: [25,50],
  second: [100,150]
}

var list = '';
$('#parent>div').each(function(ii,div){
  list += $(div).attr('class')+': '; 
	list += $.map($(div).find('input'),function(el){
  	if($(el).is(':checked')) return parseInt($(el).val());
  }).join(', ')+'; ';
});
alert(list);