output-child.bicep

resource resMyExistingVnet 'Microsoft.Network/virtualNetworks@2021-08-01' existing = {
  name: 'my-exiting-virtual-network-name'

  resource resMyFirstSubnet 'subnets' existing = {
    name: 'my-existing-first-subnet'
  }

  resource resMyOtherSubnet 'subnets' existing = {
    name: 'my-other-subnet'
  }
}

output outFirstSubnet string = resMyExistingVnet::resMyFirstSubnet.id
output outOtherSubnet string = resMyExistingVnet::resMyOtherSubnet.id
output outVnetId string = resMyExistingVnet.id