Looking for a motive. That only works with humans. It doesn’t work with subhuman psychopaths. They don’t need a motive.
Let’s see what the defense says. Will they claim the baby called the murderer a racist name?
Two possible motives:
The mother profiled them as not your ordinary homeless in need of a handout when she said NO.
And the baby dissed them by sleeping through the entire episode and not being intimidated by the thug's big moment.