It should be saliva proof. Should have good tune for number 9 as most numbers start with 9. Parents could pre-feed numbers and if baby cries too much it will dial parents numbers automatically. Should sing lullabies every 2 hours, should sense body temperature of the baby, coughing etc. Overall a design that could tell the parents what the baby's health condition is.

The 2 year old would definitely not use the cell phone as a cell phone. It would be more of a toy item. The kid must have seen elders talk on the phone and have got attracted. So, it would be of a design similar (might be of a bigger size) shape. It should be of a good material which is not harmful as kids typically put them in their mouth. Featurewise there would be audio and optical response on button clicks.