The neighbor kid was showing off his brand-new bicycle to his friends.

Literal

Next [of-の] child [subject-が] friends [to-に], brand-new [of-の] bicycle [object-を] was-showing-off.

見せびらかす is a compound verb: 見せる ('to show') + びらかす (intensifier) — 'to show off ostentatiously.' Carries a negative nuance of deliberate flaunting. 新品 ('brand new, fresh from the box') is the nominal form. Vivid, slightly disapproving.