John Piper answers:
Spurgeon was concerned about the emphasis of telling children to love Jesus rather thantrust Jesus. He expressed it like this:
Many [distort the doctrine of justification by faith] when addressing children, and I notice that they generally speak to little ones about loving Jesus, and not upon believing him. This must leave a mischievous impression upon youthful minds and take them off from the true way of peace. (Lectures to My Students, Vol. 2, 1889, p. 270)
It is a legitimate concern. Trust is more concretely demonstrable for children than love. A little child can be told to jump from the fourth step and daddy will catch him. “Trust me. I will catch you.” They can grasp that at two years old.
But what it means to love Jesus is not so easily demonstrable. Loving Jesus is more emotionally complex. It includes perceiving the qualities that make Jesus a beautiful and excellent person, worthy of our highest admiration. It involves treasuring Jesus for perfections that set him off from all others. This is not as easy for a child to grasp.