What does society need to do to stop the incidence of a biological parent's SO killing the non-biological children.

Asked by msh (4270) January 12th, 2016 from iPhone

Another child’s murder was solved over the weekend. The body of the 21 month old boy from Florida has been located after the boyfriend of the mother led police to the site where he had left the boy’s body. Police found the dead child on top of a trash heap in the man’s back yard. The remains were covered with a loose tarp hidden away in late July, 2015. Six+ months ago.
There seems to be an increasing number of stories concerning the non-biological SO of the parent, usually living in the same household, who kills the only child, or the youngest of several children This frequently occurs when the biological parent is at work. Males have it over females for doing so, but both are on the increase.
The baby mentioned above was supposedly kidnapped out of a car, according to the man’s original statements to police. after the car was ‘stolen’ the man frantically called police, causing a public search for the boy. The man even had the next oldest, a sister to the boy, only 6 years old herself, lie to the police about the incident. She witnessed the actual killing.
And Mommy? She lied. She’s arrested for child neglect, and lying to police. She chose the murdering SO over her child. The couple have now turned on each other in order to make a deal to lessen their own charges.
This type of murder is on the rise. In every state.
What needs to happen?
Why aren’t the laws and penalties more harsh than the few years given in punishment at this time?
Can you figure out why this is on the rise ?