Suspend SC is a good option for fleas. You would need to mix an IGR (insect growth regulator) with it to make sure the fleas do not reproduce. We would recommend the same with Demize EC. These products should be added to water and directly applied with a gallon sprayer to problem areas such as rugs, carpets, furniture, pet bedding, baseboards, and cracks and crevices
We would recommend using Ultracide. It contains an insecticide, as well as an IGR (insect growth regulator). This will stop the fleas from reproducing. It is safe to spray on your furniture. This will kill the flea larvae and eggs as well as the adult fleas. You will do your first treatment and then vacuum daily for 14 days and do a second treatment. Sometimes a third and/or fouth treatment is necessary.
We would not recommend spraying when the children are in the room. Once the products have had time to dry, 2-4 hours, they can return to the room(s) that have been treated.
The main thing to know when dealing with fleas is that there is no overnight fix for them, it can take multiple applications to completely eliminate them sometimes 2-3 treatments or more.
When using Suspend SC you want to use the product within 24 hours of mixing. It starts to lose its efficacy after that.
Butterflies are insects and will be affected by an insecticide like Suspend and any other product the same way the target pests like ants and spiders would be. The best way to reduce the chance of the Suspend affecting the butterflies and beneficial insects is to spray later in the day when they are not active and are back in their homes/nests, and try to avoid blooms of flowers and plants they would be using for pollenation. Most structural insects you would be targeting are not going to be landing in the same places they would be so it helps keep you from doing as much damage.