The cats in their new home

The vet told us to keep the cats inside for 3 weeks now that we have moved. They need to get to know the house first. This week, they finally could go outside. We wanted to try it first with a thing they use to walk with dogs (don't now the exact name). They were scared and wanted to go inside as soon as possible. The next day we tried it again but now they both went outside after a while.