Some do it to potentially document accidents - I know some racial minorities in my country that say they are accused of child abuse and investigated at the drop of the hat if they bring their kid to the doctor and they have any kind of bruise. I heard of a Muslim woman who lost custody of her kid for 48 hours until she was able to produce CCTV footage of her child breaking his arm in a playground accident, and not due to some act of child abuse.

So,, having a cam that catches your kid experiencing an innocuous fall wherever it may be in the house is a good security measure, particularly if the justice system comes at you preloaded with bias.