One thing to note is if their hands are cold or warm. If their hands are cold it will give lower % readings which aren't necessarily accurate. Even if their hands are above their heads it can alter the readings

Their ox sats should be over 95% ideally especially if they're little. 93-94% is okay, but they're definitely sick, but not necessarily a cause for worry especially if they're asthmatics and are a bit sick, that can be normal but they will be breathless. You don't really need to worry until they're under about 90%.