There are several excellent text books on pediatric critical care out there. AACN's Core Curriculum for Pediatric Critical Care Nursing is one, Curley's Critical Care of Infants and Children 2e is another and Hazinski's Nursing Care of the Critically Ill Child 3e is a third. They're all available through Amazon
I work both pediatric cardiac ICU and PICU. Our unit admits about 1200 children a year. For new PICU nurses, the day starts with getting your assignment (1 or 2 patients, depending on acuity) and getting report from the nurse going off. My primary survey (visual and auditory assessment from a distance) is happening while I'm listening to report. I usually do my safety checks (allergies, emergency drug sheets, ID band, some form of bagging device, oral airways, suction, oxygen, pump settings and drug concentrations and any other safety-related item specific to the patient) and a quick look at the care plan to see if I have any tasks (blood gases, meds, treatments) due in the first hour of the shift. While I'm doing my safety checks I usually also level and calibrate my pressure lines. Then I'll do my secondary survey, a head-to-toe, comprehensive assessment of the patient. This type of assessment is done every 4 hours and documented, plus focused assessments may be carried out more frequently (neurovitals in the trauma patient, respiratory assessment in the asthmatic etc). Once I've completed my assessment and documented it plus the hourly vital signs and fluid data, and carried out any tasks that may be required in the first hour, I might then read the progress notes or operative reports for a more complete picture of the patient. Many kids in the ICU will require frequent observations and interventions, such as titrating infusions to meet vital signs parameters, checking blood gases or blood sugars and adjusting therapies accordingly, monitoring urine output, bleeding and level of consciousness, administering meds and blood products. Your shift will be partly routine, partly observation, partly planning for the unexpected and occasionally partly pure terror... Most days are reasonably predictable, but not all of them. You may start out with two very stable kiddos, transfer them both to the ward and then admit a kid in septic shock who requires your every resource. Just remember that you're part of a team and you're never going to be totally alone with a very unstable patient. Experience is the best teacher so don't expect to know everything about everything or that you'll function at the same level as more experienced nurses around you do. Ask lots of questions, ask for help when you need it, offer help when you're able and you'll be fine.