What if you were to obtain/print off literature about the adverse health effects and leave it with them?

I want to reassure you that you are making the right decision regarding your children. Their health is the concern.

The conversation you have with your mom may need to look like this...

Acknowledge that at the present circumstances she feels are not sufficient enough to require assistance. Ask then at what point must the infestation reach that she would deem the problem IS bad enough (you may need to concede here). Come to agreement then as to what it will come to and limits reached that steps will be taken. Have her reaffirm this agreement. It could sound like, "And so Mom, we are in agreement that....."