Make their water only deep enough to set their butts in once they have their legs.
Get a 10 gallon aquarium with a screen lid. Put a nylon or tightly-woven tulle over the lid.
Flightless fruit flies are the easiest way to provide them with food and the easiest way to put their supplements on them. The nylon will keep them from getting out. The 12x12x18 Exo terra tank's screen lid has a fine enough screen that the fruit flies can't get out.
The froglets will no longer eat pellets or fish food once they are out of the water. They will want insects.
You'll need to get some calcium with vitamin D3 powder and some amphibian/reptile multivitamin powder supplements. Lightly dust the insects with calcium/D3 2 days a week and use the multivitamin one day a week but not on the same day as the calcium.
Use a small baggie and put a little pinch of the supplement in. Tap a few insects in and gently shake to lightly coat the bugs. It should not be a thick coating. Then gently tip the baggie at and angle over their tank and the flies or tiny pinhead crickets will slide out. Be careful not to get the extra supplement powder all over in the tank.
You can also use springtails, but they're pretty small and depending on the size of the froglets you might need a lot to keep them full.
How big would you guess the froglets are from nose (snout) to butt (vent)? This will help us to determine which size of food will work for them.