YOu need some "bait stations", about $10 each.
They have a hole about rat size; nothing bigger can get in.
There are two major kinds of poison, granulated (Dcon) and green bait blocks.
Put some of each in each station; at least 4 around the perimeter of the house with a concrete block to hold it in place.
The rats under the house will come out, probably every night to forage.
Check the stations in about 10 days.
If the poison is half gone, your vermin problem should be well under control.
If the poison is ALL gone, refill them.
Done right, it would take a VERY unusual situation for kids or larger pets to be affected.