There are those who attempt to cast doubt on the Visitation of Moroni to Joseph Smith stating that if an angel appeared to Joseph in his bedroom then why didn't his siblings see what was going on? So you are telling me a room full of kids just didn't notice an Angel of God glowing like a 500 watt light bulb speaking with Joseph like one man speaks with another?
Yes and there is precedence for just such a thing. In the account of Jasher we find that when Abraham went to offer up Isaac God established a sign to designate the mountain that the sacrifice of Isaac was to take place:
40 And Abraham went with Isaac toward the place that God had told him.
41 And on the third day Abraham lifted up his eyes and saw the place at a distance which God had told him of.
42 And a pillar of fire appeared to him that reached from the earth to heaven, and a cloud of glory upon the mountain, and the glory of the Lord was seen in the cloud.
43 And Abraham said to Isaac, My son, dost thou see in that mountain, which we perceive at a distance, that which I see upon it?
44 And Isaac answered and said unto his father, I see and lo a pillar of fire and a cloud, and the glory of the Lord is seen upon the cloud.
45 And Abraham knew that his son Isaac was accepted before the Lord for a burnt offering.
46 And Abraham said unto Eliezer and unto Ishmael his son, Do you also see that which we see upon the mountain which is at a distance?
47 And they answered and said, We see nothing more than like the other mountains of the earth. And Abraham knew that they were not accepted before the Lord to go with them, and Abraham said to them, Abide ye here with the ass whilst I and Isaac my son will go to yonder mount and worship there before the Lord and then return to you. (Jasher 23)
There are scriptural accounts which demonstrate that the presence of a heavenly experience is not always visible to unintended third-parties. An experience with one man will leave another man standing right next to him without any knowledge or experience of the event. Another example of this is the prophet Daniel who alone saw the vision and his companions did not: In Daniel 10: 7, "And I Daniel alone saw the vision: for the men that were with me saw not the vision; but a great quaking fell upon them, so that they fled to hide themselves."
It is true of the vision in Joseph Smith's childhood bedroom, where others were also sleeping when the angel Moroni appeared. See JS-H 1: 30, "While I was thus in the act of calling upon God, I discovered a light appearing in my room, which continued to increase until the room was lighter than at noonday, when immediately a personage appeared at my bedside, standing in the air, for his feet did not touch the floor."
To behold the things of God we must be quickened by the spirit of God. One wonders if someone had come upon the Messiah and his apostles at the Mount of Transfiguration would they have seen anything. In the Book of John 12: 27-29 the voice of God speaks and yet while some heard a voice others heard only thunder:
“Now my soul is deeply troubled. Should I pray, ‘Father, save me from this hour’? But this is the very reason I came!
Father, bring glory to your name.” Then a voice spoke from heaven, saying, “I have already brought glory to my name, and I will do so again.”
When the crowd heard the voice, some thought it was thunder, while others declared an angel had spoken to him."
God works in patterns. In understanding how God works we must also investigate his patterns. Shalom.