In the Old Testament being fruitful is directly called a blessing over 20 times. For example in Genesis it says, "And the Lord blessed them (Adam and Eve) and said be fruitful and multiply."
Here I am with three little children. Days are difficult. Nights are not always easy either, especially when sickness is involved. Mealtimes are messy. Discipline seems never ending and never seems fruitful. Energy is lacking. Housework is always behind. Phone calls are more stressful than fun. Crying and whining is loud and consistent. Yes, there are joys, but I have many times heard the question posed, "How can this be a blessing?"
Hearing this question has caused me to meditate on the meaning of blessing. I think that we, as Americans, automatically assume a blessing is something that makes life easy and gives us constant joy. In other words a blessing is something that's there to serve us. Seeing that in writing immediately sends up red flags. Jesus said He came not to be served, but to serve. Shouldn't that be our attitude? I think the true meaning of a blessing is something that brings us closer to God.
Now, I re-ask the question: How are children a blessing? When we first see our new born babies we can praise the Creator for this little one who is fearfully and wonderfully made. On a daily basis they bring us joy in little ways that can bring about thanksgiving. In all of the difficult stages we have a choice in how to get through them. I can say with confidence that the best way to get through the trials is with prayer. Prayer does not make the difficulties suddenly disappear and it doesn't always make us feel better, but it ultimately draws us closer to God and that is what a blessing should do.