Hi! I don't work in an ER, but I have friends who work in a kid's ER. So here is a little of what I know--maybe some people can add to this.
The answers to your questions really depend on the hospital you work at. For example, my hospital does not do major trauma, so the lack of trauma tends to slow down the pace of the ER a little bit. At our ER, there is a big mix of acuity. Kids tend to need medical attention for things that an adult might wait out the night/weekend and see their regular doc. So in the ER, you will definitely see a lot of ear infections, RSV (respiratory infection), gastrointestinal illnesses (read vomiting, diarrhea, and dehydration), etc. You will also see kids who are more critically ill or have a history of chronic, complex health problems. This means that the pace can vary from moment to moment. One minute you are getting ready to send home a two year old with an ear infection, and the next minute a very sick patient comes in by ambulance, and lots of people work together quickly on this new patient. There are busy times of the year--winter for almost any peds ER, summer too if your ER does burns and trauma. There can be times where there are few patients in the ER for periods of time, and there are times where the waiting room is jammed. This is a specialty that requires flexibility and willingness to go with the flow, but also willingness to be constantly learning because you're always seeing new things. Kids will be out of their element and often tired, hungry, hurting, etc., and parents may be very stressed out--so a big part of your job is trying to make them comfortable and (reasonably) calm. Your relationships with patients and families are very short-term (hours), although there are some children who you may see on a frequent basis.

If you enjoy the unexpected, function well in a (sometimes) fast-paced environment, and enjoy helping people who find themselves in crisis (of varying levels), this could be a great specialty for you!