My little Beefsteak seedlings are no higher than 1 to 1 1/2 inches, and already the tips are turning brown on several of the leaves. What could this possibly be?
Wind burn, sun burn, bubonic plague!!
Could be lots of things - we need more info about how you are raising these seedlings. Amount and type of light, soil, watering schedule, and room temperatures.
If it's just the tips then fertilizer burn or overwatering are the usual culprits, but if it turns into browning along the leaf margins, that may be a different story.
As Gary said, need more info about what they're in, what you've done to them, and more.