The tabernacle was the place where Israel could go to meet with God, so if Samuel grew up in the presence of the Lord, it means that he grew up in the vicinity of the tabernacle. There is also a suggestion that, in contrast with Eli’s sons, Samuel had a proper respect and reverence for the Lord.
21 Indeed the LORD visited Hannah, and she conceived and bore three sons and two daughters. And the boy Samuel grew in the presence of the LORD.