If it is not clear from the description/amenities list whether there is extra bedding or cots for children, then you can message the owner to ask them if it is available or possible for them to supply.

Firstly, you will need to login into your Search and Stay account then select 'Messages' from the left hand toolbar.  Here you will see your current bookings, you will just need to select your booking and then you will be able to send a message to the owner via the message panel.