It is extremely toxic. Put it up somewhere high (even in the attic), or keep it in a locked garage or cabinet. You should not need to use it very often, so if it's a bit inaccessible to you, it's not that big of a deal.
You should store it in a cabinet, probably the one beneath the sink. To keep the kids and animals out, you should install a child safety latch. You can get these at a home improvement store.
Store it in a locked cabinet up high so there is absolutely no chance your kids or pets can get to it. Keep the key to the lock hidden so your kids won't just get curious and decide to open the cabinet for fun. Ideally it should be stored in a room they don't spend a lot of time in.
