Worried about my white's tree frogs

[noodlebread]

Hi, I'm not completely certain if I'm posting this correctly, but I am very worried about my two juvenile white's tree frogs. I am completely new to frogs.

I have two juvenile white's tree frogs that were purchased about 4 weeks ago just before Christmas. They seemed to be fine, however I feel like they aren't eating. They always seem to be in the corner of the tank and don't seem to get onto the ground. When I first got them, they seemed to be very active and attempted to eat. Now, they don't seem to be eating the crickets anymore. I've tried dangling a cricket in front of one of them, but he did not eat it.

They seem to take on a brown-ish colour, and their underbelly is a light red / pink. They also seem to be very thin for a white's.

The tank is usually at a temperature of 70 - 81 degrees celsius. I have a heating lamp which is usually kept on one side which they enjoy being under. I mist their tank regularly.