This week’s half-million dollar apartment building fire in suburban Des Moines was likely caused by children left home alone while their mom went on a beer run.The fire Tuesday afternoon gutted the building at Crestland Apartments in Clive, leaving four people hurt and 16 homeless. Clive’s fire marshal Tony Collins says three children were left in one apartment by their mother, who witnesses say, went to the store to buy beer. Collins says at least one of the kids, ages two, four and six, apparently got hold of a torch and started the fire that quickly spread. The kids were trapped by the flames and the mother, upon returning, broke a window to rescue them. No charges have been filed. The woman’s name is being withheld.