Create Fn::GetAtt references between cloudformation templates

I'm creating custom cloudformation templates and I understand that you can use your outputs to call in parameters from other templates into other templates using the Fn::GetAtt feature.

Currently my VPC template has, for example;

"ParentVPC" : {    
    "Description" : "VPC ID",
    "Value" : { "Ref" : "VPC" }
},
"DBSubnet01" : {
    "Description" : "DB Subnet 01",
    "Value" : {"Ref": "DBSubnet01"}
}

So from my application template I'm wondering how I would call those in as parameters. I have tried;

"ParentVPC" : {
     "Type" : "AWS::EC2::VPC::Id",
     "Description" : "VPC of Parent"
 },
"DBSubnet01": {
    "Description" : "Reference to VPC DBSubnet01",
    "Type" : "List<AWS::EC2::Subnet::Id>",
    "ConstraintDescription": "must be list of EC2 subnet ids"
}

Any suggestions welcomw