Map<String, String> childListMap = new Map<String,String>();
List<Schema.Childrelationship> childList = Schema.getGlobalDescribe().get('Account').getdescribe().getChildRelationships();
for(Schema.ChildRelationship cr : childList){
    //system.debug(cr.getChildSObject());
    //system.debug(cr.getField());
    childListMap.put(String.valueOf(cr.getChildSObject()),String.valueOf(cr.getField()));
}
System.debug(childListMap.size());
for(String s : childListMap.keySet()){
    System.debug('Obj: ' + s + ' Field: ' + childListMap.get(s));
}

String obj,field;
String queryString;
Map<String,List<SObject>> objMap = new Map<String,List<SObject>>();
for(String s : childListMap.keySet()){
    obj = s;
    field = childListMap.get(s);
    queryString = 'SELECT ' + field + ' FROM ' + obj + ' WHERE ' + field + ' = ' + accId;
    List<SObject> objResult = Database.query(queryString);
    if(obj.size() > 0){
        objMap.put(obj,objResult);
    }
}