def get_children(res,key):
    """
    Returns a list with all keys in res starting with key
    
    Parameters
    ----------
    res : dict
        results dictionary
    
    key : string
        a search key
        
    Returns
    -------
    keys : list
        list of keys that start with key
        
    Examples
    --------
    >>> get_keys_with({'time':[0,43200,86400],'A.B':[1000,5000,2000],'A.C':[2000,8000,3000]},'A')
    
    """
    
    if key == '':
        return res.keys()
    else:
        keys = []
        for k in res.keys():
            if k.startswith(key):
                keys.append(k)
                
        return keys