I have cruised a number of lines and times with my kids but they were definitely older than 4 and 7 when they joined us in a balcony cabin. Their are chairs on the balcony. A four year old (if the door is accidentally left unlocked by the room steward or yourselves, could definitely climb onto a chair and fall over. I would not cruise in a balcony cabin with a 4 year old. An outside cabin with a picture window will allow you to have light. My youngest boy was 10 before we let him in our balcony cabin. We knew he would not stand up on chairs. My advice.