Answer: See explanation
Step-by-step explanation:
The meaning of elevated in this sentence “The number of kids in Flint with elevated lead levels in their blood had nearly doubled between 2013 and 2015.” is "above average", "greater than normal" or "higher ".
The sentence simply means that the number of kids in Flint with that has higher lead levels or lead levels that were above average had nearly doubled between 2013 and 2015.