It sounds like you are commiting yourself to a fellowship pathway (at least 5 years of postgraduate training). I think you need to explore the significant differences between pediatric anesthesia and neonatology. Making a poor decision could be costly.
Neonatology (and pediatric critical care) involves extended care of sick children. You will follow these kids over weeks to months. At times it can be intense trying to manage a critically ill child. Most kids these days get better. Some will spend months in the ICU and die (or transfer out with a disabling illness). The lifestyle is demanding. To be happy in a critical care field you need to come to terms with the lifestyle. It is hard to plan a schedule when you are responsible for the care of critically ill patients. Talk to practicing intensivists in different environments about the hours. If the commitment sounds too rough, you should question your interest in a critical care field.
Pediatric anesthesia focuses on episodic care of healthy and ill children. You may get to care for some children repeatedly but usually just short-term. Anesthesia can be a fast paced environment with complex decision-making. I enjoy caring for sick kids, but I also enjoy not having long-term responsibility for their treatment. I would say that overall my lifestyle is somewhat better than that of an intensivist (financial and schedule). I do, however, work some nights, weekends, and holidays. I take both in-house and call from home. (This will vary by hospital or group)
The pathway to either field will be different. I think neonatology is a 3 year fellowship (in addition to a 3 year peds residency). Anesthesia Residency is 3 years (in a addition to a prelim/intern year). Most of anesthesia training will focus mainly on adults. Pediatric anesthesia fellowship requires one year after which you could be exclusively a pediatric anesthesia provider.
If you think 5-6 years of residency/fellowship training is not enough, consider this next pathway. I know many pediatric anesthesiologists who actually did a pediatric residency followed by anesthesia residency and/or pediatric anesthesiology fellowship. Some even practice both anesthesia and critical care.
If you are really undecided, perhaps you should pursue a pediatric residency. This would allow you more exposure to the NICU and PICU. Then do a pediatric anesthesia elective. Perhaps you decision would be easier with more experience.