I had 3 guinea pigs and now I have a rabbit. Both these animals often damage their legs.

If it happened, first of all you must recognize what was damaged. If your pet has blood on its legs or it licks them your rabbit or guinea pig pulled out its nail. Take your pet and find out if the nail was pulled out completely or broken. If it is broken you should remove the broken part with scissors - it will be better if you have special scissors for rabbits (they're good for guinea pigs and cats too). Be careful! Rabbits and pigs have veins inside their nails! Never cut off too much!

in any way treat pet's skin and bandage its leg.

If there is no blood touch all legs of your pet. Don't push - you may damage your animal if its leg is broken! Your pet will try not to let you touch the broken leg.

Look how your pet walks. If it can't stand on one leg it's time to go to vet.

How to prevent your pets from damaging legs?
First of all never leave the chest opened, especially if you have a rabbit - they often damage legs while jumping out. Also you should look after pets while they are going for a walk.
Try not to let pets walk on carpets.