Logs generated by Lambda Functions

You can query the CloudWatch Logs API and see how much storage each log group is consuming: aws logs describe-log-groups

For each log group the output will look like:

"logGroupName": "/aws/lambda/FunctionName",
"creationTime": 1573030762692,
"metricFilterCount": 0,
"arn": "arn:aws:logs:region:accountnumber:log-group:/aws/lambda/FunctionName:*",
"storedBytes": 148153072