I don't have to tell anyone here that children are messy. Clothing will stain, and you will have to deal with it. Such is life.
However, this handy recipe will get a LOT of stains out of clothing. I have used it successfully on all sorts of stains. It hails from The Complete Tightwad Gazette, which I confess is one of my all-time favorite books. (I know, surprise, surprise. I can't help it; it's full of great tips and recipes and inspiration. Some naysayers complain that it is outdated, and I do confess that it's amusing to read discussions of records vs. CDs or whether or not one should buy a home computer. However, the principles are timeless even if the examples are not.)
The official recipe is 1 cup Clorox II + 1 cup Cascade powder + 5 gallons of the hottest water you can get from your faucet. Soak several garments overnight, then launder as usual. It is not recommended for delicate fabrics or items that are not colorfast.
I personally use Oxi Clean (or the Sun or Dollar Tree equivalent) and store brand dishwasher powder for this recipe. I also use less of the powders and less water. Still, it works--particularly on food stains.
I used it quite successfully last week on this:
Dawn dish soap (or equivalent) also makes a goo pre-treater for stains, particularly greasy ones. Apply directly to the stain. Launder as usual.