Having children who are now older and having dealt with health issues related to toxins, I tend to be fairly cautious about using plastic, particularly in the microwave.
Here's info from Mercola.com on this topic, which doesn't have the biases that the FDA or plastics council might:
http://www.mercola.com/2005/jul/5/food_storage.htm
With the following summarizing, what is considered safer if you choose to use plastic:
" If you feel you have to use plastic, choose items that contain one of the following materials, none of which are known to leach harmful substances:
Polypropylene, designated "#5 PP"
High-density polyethylene, designated "#2HDPE"
Low-density polyethylene, designated "#4 LDPE"
"
So, I would recommend transferring the food from other numbered containers into a glass or ceramic container for heating in the microwave. I personally would stick with the baby foods in glass jars, ideally the organic ones. Unfortunately, our kids are growing up in a very toxic environement and we can reduce their toxic load by feeding them organic as much as possible.