A little boy is standing in front of a wedding party laughing.
There is a bride and groom behind the little boy.
"wedding " implies "bride and groom " and  "in front of " could mean the same as "behind " depends on the observer's direction.
a bride and groom are part of a wedding party. If the little boy is in front of them, it means the bride and groom are behind him.
The bride and groom is in the wedding.