Here are some videos specifically for pediatric ultrasound placement:
Ultrasound Guided Pediatric IV Placement In Under 10 Seconds, YouTube video, 0:25, from the Pocus4Peds Channel.
Ultrasound Guided Central Venous Catheters in Children and Neonates, YouTube Video, from Noreddine Bouarroudj
And here are some general ultrasound IV placement videos:
ultrasound guided peripheral IV course by Siegfried Emme, YouTube Video, 25:31, from Siegfried.
Ultrasound Guided Peripheral IVs, 19:02