I don't recommend it
Any foreign ingestion can catch in the swallow tube, blocking fluid & food intake.
That might require retreival in the or. If it makes it into the stomach it may pass thru the gut within 3-5 days. I wouldn't expect lego's to show up on xray unless the company put something in the plastic for this reason. Feeding
the kid stewed okra soon after the ingestion can wrap it up & smooth passage.