There are some great resources out there. The Environmental Group publishes the "dirty dozen" list, and you can actually download that and put it in your wallet and refer to it. There is also "the clean 15." So the "dirty dozen" are foods that you really want to avoid, unless they are organic. The "clean 15" are the ones that you can pretty much get away with eating conventional or organic; whatever you can afford, whatever you want to do.
My rule of thumb, when it comes to fruits and vegetables, is the thinner the skin and the more delicate the fruit; the more likely it is to have a high level of pesticides in it. Anything you can peel, for example, like an orange. If you have the choice between choosing an apple and an orange, choose the orange because you can peel away that rind which contains most of the pesticides.
Today, apples -- We always think, an apple a day, keeps the doctor away -- Apples contain over 56 different pesticides, which are in one fruit. You really need to be aware of these things; especially if you are feeding your kids. Look for those downloadable lists, think about the rule of thumb.
Also, when you are considering what you can afford, and what you can't afford. I like to use the example of milk. The difference between a gallon of conventional milk and a gallon of organic milk is about $2.00. My kids go through that in about a week. The average American spends an average of $2.00 a day, on coffee. I think to myself, is it worth it to me to give up a latte, so that my kids can have a gallon of milk for a week? Absolutely, it is.
Everyone makes their own choices; but when you put it in that type of perspective, it really helps make the case for buying more organic food for your children.