ingenuous

Naive and trusting.

Demonstrating childlike simplicity.

"Do you mean to say you didn't leave your wife for another woman?" "Of course not." "On your word of honour?" I don't know why I asked for that. It was very ingenuous of me.

Unsophisticated; clumsy or obvious.

The apparent contradictions in his behaviour should therefore be discounted as ingenuous attempts to extricate himself from the consequences of an intellectual position which he once adopted but was never really his by intimate conviction.

[…] Semitic agitation by stating 'the truth' in terms of facts and figures, the practice of self-criticism represented a well-intended but ingenuous effort to defend Jewry against anti-Semitism.

Unable to mask one's feelings.

Straightforward, candid, open, frank.

[H]is Grace’s Man at his club, in company doubtless with other Men of equal social rank, talks over his master’s character and affairs with the ingenuous truthfulness which befits gentlemen who are met together in confidence.