You shouldn't choose a career based on flexible hours unless you are supporting a child or have another legit reason. Both careers have busy seasons and can have hectic schedules. It really depends on what aspect of interior decorating you are looking into, and what branch of childcare you are interested in.
I would say... an Interior decorator. It is always easier to deal with "dead things" (objects) to human beings specially children. Moreover if you are a freelance in the company of the interior decoration then you can do your work from home, I mean like making the designs.
No. Not really. An interior decorator has a lot more flexibility. Although you realize you're talking about two different professions which need different educational levels, have different levels of pay, and do totally different things.