<?php

class cAbstract
{
    public function zrobCos()
    {
        $this->metodaChilda();
    }
}

class Child extends cAbstract
{
    public function start()
    {
        $this->zrobCos();
    }

    protected function metodaChilda()
    {
        echo 'elo';
    }

}

$obj = new Child();
$obj->start();