Forests enter the battlefield as land creatures, and abilities that trigger whenever a creature enters the battlefield will trigger. Because you haven't controlled these creatures since your turn began, you can't pay the cost of their mana ability.

Saprolings enter the battlefield as land creatures, and abilities that trigger whenever a land enters the battlefield will trigger.

Each Forest has the ability ": Add ."

Each Forest and Saproling will have the card types creature and land, and the subtypes Forest and Saproling. Each subtype maintains its correlation to the proper type: Forest isn't a creature type and Saproling isn't a land type.