Large claw broke off

Question
We recently got 2 hermit crabs for my kids.  I woke up this morning to find that one of them had broken their large pincher off.  Can this crab live without his large pincher?  I am new to the whole hermit crab world, and am trying to make as suitable a home for them as possible.  We purchased a 10 gallon glass aquarium, with plastic hood and light.  The base is stone, with a bottom heater.  I have been trying to keep the humidity level above 70 percent and the heat in the tank between 75 and 80.  I only use bottled spring water in their water dish, and use a combination of "web" bought foods.  I read on a website that they love to climb so I bought a Habba tree and another ceramic tree for them to climb on.  I also take them out of the tank every so often to crawl along the floor or my arms in an effort to acclimate them to me.  Is there anything else that I should be doing, or anything listed above that I should not be doing.  I really am getting into these crabs as are my children.  Any advice you could give me would be greatly appreciated.  Thank you for your time.

Answer
Dropped limbs is a sign that your crab is stressed.

You need to replace the gravel with either damp sand or coconut fiber bedding (like eco earth). You also need to provide ocean style salt water in addition to the fresh water.

If your crabs are new, they shouldn't be handled for the first several weeks as they destress and acclimate to your tank.

Also avoid handling them if you've been wearing perfumes/colognes, lotions, etc.

The good news is that the crab can regenerate the big pincher but will be more likely to do it if it has the proper substrate.