
Hi Mommabrooks, WELCOME to FISHLORE! Hopefully we can give a hand to help you through. Don't feel bad, everyone is a beginner sometime, and we all have gone through just what you are today.
First: You need to do a water change tonight! If you aren't set up to do it, with water conditioners, you need to draw enough water to change about 50% of the tanks water and let it set over night. You can't put water in right from the tap, unless you have untreated well water. You always try to match the temperature of the tank with water you put in. If you have conditioner to take out the chlorine, go ahead and change 50% of your water.
Second: The list of things to get if you don't already have it,
Syphon tube with vacuum attachment, API Master freshwater test kit.
Your tank needs, filtration, heater, themomoter, Air pump and airstone.
How big is the tank?
You don't say you cycled the tank before introducing fish. The fish are probably suffering from ammonia poisening.
Now that the pleco is dead, don't add ANY MORE fish until the cycle is complete. It will be a lot less traumatic for you and your children.
When you do test your water, post the results and we can tell you more.
I see Omorrokh has also posted. Sort all this out and we will try to help further.
