I would not run a high humid environment personally....BUT I would offer a warm humid hide/area for the baby....you can do an entirely humid enclosure but you will need to pay very close attention to the temps so that it never ever drops below 80 degrees....HOWEVER, for this species I would offer a warm humid hide instead...
Offer really deep substrate (at least 5-6 inches deep) of earthen material so that the tort can dig in as they like to do this....
As mentioned above,the humid hide is a great idea.
I like to keep my enclosure between 50% and 70% humidity with a basking spot at 95 degrees and about 75 degrees on the cool side. With the younger Torts its a good idea to go a little warmer for the cool side.
Where I'm located, in eastern VA, it is difficult to get humidity lower than about 45% unless you have a very dry substrate. So offer your tort a choice of a humid hide and a somewhat drier area in the rest of the enclosure. Giving your tort choices of humidity and temperature allows them to self regulate.
I like the mix of topsoil and coco coir for substrate.