I can only respond based on U.S. slavery but murdering a slave wasn't regarded as "theft" per say.

Before the late 18th century there was little legal sanction for the assault or murder of slaves but laws eventually developed, and differ slightly based on individual state laws.

Typically murderers of slaves could be imprisoned for about a year for their crime but there were so many loopholes to protect murderers from this... such as if the murder was deemed as an appropriate response to some form of infraction of the slave... which could be very minor and totally down to the imagination of the white slave-holder as African Americans were unable to testify in court. More likely, if a white person killed another's slave they would arrange a personal debt or similar - this happened if slaves hired out were "damaged" by their loaners.

In terms of killing their own children, infanticide is a really interesting area of scholarship at the moment. It seems that the practice was not common as enslaved people loved their children and placed high value on their family networks. Also, you are right, they may incur infraction from their masters or mistresses if discovered. American slavery was legally defined by the mother's status, so even children of white slave-holders remained enslaved. However, there is evidence of the use of certain abortifacients (such as chewing the cotton root) and instances of infanticide. The cases I have read,at least, seem to often be women whose children were the outcome of rape.

I hope that is some interest to you although I know this isn't your primary area of focus!