Albert Barnes Commentary 1 Samuel 2:18

"But Samuel ministered before Jehovah, being a child, girded with a linen ephod." — 1 Samuel 2:18 (ASV)

Girded with a linen ephod - This was the usual dress of the priests. It does not appear whether Levites wore an ephod properly. Possibly, it was a mark of Samuel’s special dedication to the Lord’s service that he wore one (see the marginal reference). The ephod was sometimes used as an idolatrous implement (Judges 8:27).