Most Mormons would probably be offended by the question, because they believe and say that they are. Yet this is a difficult question for others, for a variety of reasons. In defense of the question, which offends so many Mormons, Mormons should be reminded that they do not believe that any church is Christian but their own. A resultant spiritual darkness covered the earth for centuries until one morning in the spring of 1820 when God the Father and his Son, Jesus Christ, appeared to a young boy named Joseph Smith and initiated a restoration of all the truths, powers, and priesthood authority of the ancient Church. If Mormons don't believe your church is really a Christian church, it's certainly fair for you to ask whether or not theirs is.
Sacramental validity requires proper form, matter, intent, and minister.
The proper matter for baptism is water. A person cannot baptize himself. The matter is proper, Mormons immerse in water. Because the intention required for validity is minimal, it must be assumed that Mormons have that. And finally, because any person may validly administer the sacrament of baptism, Mormons have proper ministers.