Altered mental status in children can be subtle. Look for age-specific behaviors that range from irritability to anger to sleepiness to decreased interaction.
In the altered child, anchoring bias is your biggest enemy. Keep your mind open to the possibilities, and be ready to change it, when new information becomes available.
For altered adults, use AEIOU TIPS (Alcohol-Epilepsy-Insulin-Overdose-Uremia-Trauma-Infection-Psychosis-Stroke).