This isn't necessarily true. 

Ideally, you would have a spare bedroom for an adopted child. This is particularly important when adopting older children or if you have children already, as relationships with existing children in the family can take time to settle down. It may be possible, however, to consider a very young baby moving in with a family with no additional bedrooms (sharing with parents) so long as there is a clear plan to provide the child with a bedroom of their own or with a sibling in the future.