Until your next turn, all lands you control become 2/2 Elemental creatures with reach, indestructible, and haste. They're still lands.
4/27/2018 Sylvan Awakening doesn’t untap any of the lands that become creatures.
4/27/2018 Sylvan Awakening affects only lands you control at the time it resolves. Lands you begin to control before your next turn won’t become creatures.
4/27/2018 The lands affected by Sylvan Awakening stop being creatures as your next untap step begins, before you untap your permanents. If this causes any state-based actions to become applicable, or if any abilities trigger, those are handled during your upkeep.