The one downside to placing small froglets into a large viv immediately is that you will be challenged to monitor their feeding. Very young leucs have a tendency to hide when placed into a new environment (at least in our experience) which doesn't help matters.
Your froglets will probably be 1/4 to 1/3 the size of adults if they are well started.
I would recommend that you go with a shoebox or 10 gallon viv setup for them, at least for the first couple of weeks. Either of those setups can be reused for other purposes down the line. Yeah it's a bit inconvenient to transfer them to their permanent home down the line but it's worth the hassle to know that the froglets have made the transition to your home and are feeding well, etc.
Good luck and enjoy your froggies!