Marriage between man and woman is essential to His eternal plan
(by Amy)
I would start out by saying something like ...
Children this year we've been talking about a special plan that we chose to follow - if you know the name of it can you put your hand on your heart.
 
Then talk a little bit about the plan of salvation or plan of happiness.
To fulfill the plan of happiness each man needs to find a good woman and get married hopefully in the temple. To live our lives and never share them with a husband or wife would be like making a cake and never baking it. We wouldn't get to experience all of the good things that life should bring and we wouldn't be keeping all of the promises and commandments that we promised Heavenly Father we would do.
 
Starting with the creation of the world and with Adam and Eve marriage between a man and a woman has been a commandment and an essential part of life.
 
______________________________________________________________
Okay here are some ideas for fun things you could do with this -
 
Ask a few couples - maybe a couple that's been married the longest in your ward and a newlywed couple to come share the blessings that marriage has brought to their life. Maybe they could share how their spouse helped them through school, or raising the children, or how when they would come home each night from work the peace and joy the felt coming home to their lovely wife and happy children.
 
Another possibilty for the senior primary - write a list of men from the bible and church history and a list of their spouses (not in the same order) if you only did biblical ones you could put the scripture references down the middle - challenge the kids to look up the scripture and then pick a child to connect the man to the scripture and then the right wife to the scripture.
 
Another possibility would be to write down things a daddy does and things a mommy usually does on hearts - hide the hearts around the room - have the kids bring the hearts up and discuss how a daddy and mommy sometimes do the same kinds of things to bless our homes but sometimes there are things only a dad can do or only a mom can do that help our home to be happy.
 
Another fun thing you could do on this day - is have the kids make their parents a valentine thanking them for being great moms and dads and thank them for giving them the blessing of good parents like Nephi. Of course if your ward has a lot of children from single parents you would adapt this as you feel prompted to do.
 
Amy