No, heaven isn't a myth or fairy tale. Heaven is real -- more real than the ground you walk on or the stars you see at night, because some day they'll all come to an end, but heaven will remain.
How do I know heaven is real? I know it first of all because Jesus told us it's real -- and His word can be trusted, because He cannot lie. He said, "In my Father's house are many rooms; if it were not so, I would have told you. I am going there to prepare a place for you" (John 14:2). Just as God is eternal, so heaven is eternal, for it is the dwelling place of God.
I know heaven is real also because Jesus Christ came to earth for one purpose: To make it possible for us to go there. Only one thing can keep us out of heaven, and that is our sin. But Christ came to take away our sins by His death on the cross, and now He offers eternal life to all who put their faith and trust in Him. "For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life" (John 3:16).
But most of all I know heaven is real because Jesus Christ came back from the grave. Death and hell have been conquered, and heaven's gates are now open -- because of Him! Your mother knew this truth -- and I pray you will also, as you open your heart and life to Jesus Christ.