You can move them into the big tank, just make sure you keep the humidity level at 50%. Also you should be using the multi vitamin and calcium supplement, alternating these every other day so these little ones end up as healthy adults. When feeding the frogs use a dish to put the feeder bugs in so they don't get lost in the viv, and it also makes it much easier for the froglets to catch their dinner. And if you haven't read this yet Frog Forum - Gray Tree Frog Care and Breeding please do so, it may help your new found friends live a long happy, healthy life. I do recommend having lots of branches and vines for them to climb on. My neighbor added so many vines you would think they didn't have room to move, but since she had done this, they are more active than ever.

Name:  5-24-12.jpg
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Size:  122.3 KBThis is a tank I used for 3 greys, but like I said, I would fill this in with lots of vines and branches.