Freeze food in 4 oz containers?

I've been making my baby's food since she was 6 months old. I started freezing puree in the ice cube tray and now that she's a toddler, she eats bigger portions. I found that the stage 2 Gerber food plastic containers work great. I can freeze it, then the food will slide out and I can put in a gallon freezer bag. First question: Is this safe to re-use these Gerber plastic food containers to freeze food? Second question: Is there a product that has been designed for freezing and removing frozen food? I'm looking to freeze in 4 oz sizes. I tried searching on-line, but everything that comes up is 1 or 2 oz and I can't tell if those products are designed to remove the food while still frozen.