Instead of having artificial limits just have the tadpole growing be an actual danger.
Please no. It would be very unfun. Not "challenging in a fun way". Just frustrating and punishing the player for engaging with side content.
Items needed for rest I can get behind though. And limit the places where you can long rest to areas that are actually safe and/or easily defendable. (Like... in a dungeon - a room with area around it cleared would be ok, but not an open corridor with unexplored rooms nearby. Something like that. In general, maybe require the area around the resting spot to be explored - adventurers wouldn't want to sleep in a completely unfamiliar location where anything could be lurking just a couple steps from the camp.)