How do you know for certain God has called you to ministry?

I strongly feel led to Children's Ministry. I have worked in this area of ministry in many ways from just helping in the nursery to coordinating lessons and schedules in small churches. I have felt for some time the pull to ministry and will begin a master's program in Children's Ministry in only a few weeks.

I am only asking how do I know for sure because I do not want to do anything if God's not in it. I have done that before and learned how much more God knows me than I know myself.

My mother is supporting me in my venture of persuing children's ministry but others in my (Christian) family are not so thrilled. They express their contempt not in words but with what they don't say. (They avoid the subject of my classes and only ask me about how I am paying for them.)

A few months ago I had a dream where I heard God saying "do not listen to the lies of men." I'm not sure that the dream had to do with this or something else.

These thoughts also entered my mind at a comission service for missionaries at my church. When the pastor asked if they were sure that God was calling them and it wasn't the will of them or any other man; I started thinking perhaps my persuit of children's ministry is my will and not God's.

The truth is I have always had a passion for children and there is nothing better to teach them than to introduce them to God's word.