You decided to intubate a child and wisely remembered that you should also follow with an NG/ OG after intubation to decompress the stomach.  In order to avoid the blank stare when asked "what size"?  Here's a nice mneumonic about Pediatric "tube" sizes... easy as 1-2-3-4!!!  Please note ETT = endotracheal tube size.

• 1 x ETT = (age/4) + 4 (formula for uncuffed tubes)
• 2 x ETT = NG/ OG/ foley size
• 3 x ETT = depth of ETT insertion
• 4 x ETT = chest tube size (max, e.g. hemothorax)

So for example, a 4-year-old child would get intubated with a 5-0 ETT inserted to depth of 15 cm (3x ETT), a 10Fr NG/OG/foley (2x ETT), and a 20Fr chest tube (4x ETT).

Also, remember that you can use cuffed tubes in any child except neonates but the formula needs to be adjusted as follows: cuffed endotracheal tube ID (mm) = (age/4) + 3.5

References