Children’s picture book available in 1990s. Boy finds a flint arrow head in his garden. Somehow (that night?) he is magically transported back to the time that indigenous First Nations people lived on the land - he sits around their camp fire with them.
Could it be, The Garden by Dyan Sheldon, pub. 1995? The description seems to fit, though the MC is a girl…”When Jenny finds an arrowhead in her twentieth century garden she finds it holds the key to the past. In a beautiful dreamscape, Jenny discovers that the flint can bridge the gap in time between past and present America. With wonderment she meets the American Indians whose culture has been absorbed into the land her garden is built on.” https://www.amazon.co.uk/Garden-Red-Fox-Picture-Books/dp/0099501716