You are looking for an enamel based paint that does not contain zinc, lead, or chromate, and is advertised to bond with metal. Bonus points if it's labeled low/no VOC, non toxic, or child safe. I think the Rust-Oleum enamel paint is called Stops Rust protective enamel. It comes in as a spray or in a can - it's down to preference.
- Sand the pans with a fairly coarse grade sandpaper or wire brush, outside with a mask/glasses on.
- Scrub with soap and water, and rinse clean. Dry well.
- Prime, if desired - I'm not sure about the toxicity of enamel primers, you'd have to do a bit more searching.
- Paint, applying in thin layers and allowing time to dry in between coats. Take your time with this step.
- Vent outside or in an area with good airflow for at least a week to allow to gas off. Wash once more before placing in cage.