Looks like The Pediatric Critical Care: Text and Study Guide by Lucking, Maffei, Tamboro and Zaritsky got a 2nd edition in 2021. The first edition was getting a bit dated, but had a lot of rock solid principals reviewed and was a good foundational text.
The SCCM online course was helpful but depending on your available study time may not be the best tool. I find it really hard to sit through recorded lectures, particularly that were done as in-person conferences. Just not the best way for me to learn.
The good news is, compared to Gen Peds boards, the overall scope of questions are much more in line with what you will see as a practicing attending