1. Look at the bottom of the container it will have a number, the "good" numbers are#1 -PET or PETE and #2 (HDPE). These are the types that are used for some soft drink (okay the soft drinks are not "good"), peanut butter, salad dressing, ketchup, milk bottles, yogurt/margarine tubs, cereal box liners and water bottles. These are not known to leach out any nasty chemicals.
Those with #4 (LDPE) and #5 (PP) are not known to leach out chemicals but they do contain some nasty chemicals and are not widely recycled so skip those. These are used in bread and frozen food bags, some ketchup bottles and yogurt/margarine tubs.
Avoid those with #3 (PVC), #6 (PS) and #7 ("other" usually polycarbonate). Polycarbonates, often found in microwave ovenware, disposable utensils and baby bottles contain biphenyl A which is the chemical thought to interfere with our hormones. #6 contains benzene and used in some hard cups and #3 is the cling wrap around meats and cheeses from your deli.
2. If you use plastic, best to use #1 or #2. Best NOT to use any plastic with heat as that can raise the risk of chemical leakage (note above "known" is in italics because we often don't "know" everything). Avoid cling wraps if possible, especially in the microwave. Use "safe" plastic containers or wax paper bags for lunches (hard to find, locally in Los Angeles, Gelson's carries wax paper sandwich bags.)
Avoid plastic bottled water if possible, toss any scratched or damaged plastic containers and don't wash plastic with harsh chemicals.
3. Don't just think about your food containers but also think about toys your child may chew on and those really cute plates you bought at the 99 cent store or Toys R Us. Be an informed parent and read those little numbers on the back of the product. If there is no number, don't buy.
4. If you want to be 100% safe, save or buy glass containers and use those to store, freeze and microwave.
AND always recycle your plastic.
PS and yes it is a good idea to double your recipes and you can freeze in #1 or #2 plastic, just don't heat it up in plastic.