Showing innocent or childlike simplicity and candidness. (Merriam – Webster)
Lacking craft or subtlety. (Merriam – Webster)
(of a person or action) innocent and unsuspecting. (Oxford Dictionaries)
If you describe someone as ingenuous, you mean that they are innocent, trusting, and honest. (Collins Dictionary)
Honest, sincere, and trusting, sometimes in way that seems silly. (Cambridge Dictionary)
Ingenious vs Ingenuous: Correct Usage with Examples
Ingenuous and Sincere.