I'm currently a PICU fellow, so I should be able to help.
Let's break this down for general pediatricians vs your standard internist:
On the whole, yes, generally more straight forward in terms of the medical care you'll provide from one kid to the next. While there are nuances, an ear infection should usually get amoxicillin. Social situations can be VERY different however, and, at least for me, one of the things I love about peds is that the same outward problem (respiratory distress for example) has very different causes, physiology and considerations depending on the patient's age - a 2 month old is different than a 2 year old is different than a 6 year old, is different than a 12 year old is different than an 18 year old.
As for specialty care, yes, things become more complex with kids - and in some cases I'd argue more complex than their adults. I like to rib my adult cardiology friends that their job is easy - blood goes where it's supposed to which is usually not the case in peds cardiology, which explains why I end up having to take care of 40 year olds who had surgeries as infants in my Cardiac ICU at the children's hospital.
Are PICU patients easier? To some extent yes- the typical mortality rate for a PICU should be about 4%, compared to 25-40% you see in the MICU not infrequently. But again, once a patient becomes critically ill, they're going to be complex regardless if their 9 months or 90 years. And I promise you, no internist on earth wants to take care of the little 400 gram, 23 week gestation micro-preemies. I can't even imagine the look on an adult intensivists' face when you tell them they only have 60-75 ml of IV fluid to work with for the entire day!
Lastly, I'd say that the most medically complex pediatric patient can certainly eclipse the medical complexity of an adult. If you've got bad genetic substrate...well that can affect every organ system and easily involve not only numerous medical specialties but surgical services as well.
If you're trying to decide between the two fields, I'd ignore medical complexity and focus on the patients themselves. If you don't like kids (or in my case, adults), it's not going to matter what the medicine is...