But....we are all so different. Let us never equate difference with better or worse. A child is as vital to God as any adult (the simplest reason behind our Church's clear pro-life teachings) but a child is not an adult as there are clear differences - maturity, size and abilities can come to mind here.
But, both are capable of loving God, enjoying life and finding complete happiness to the best of their ability and capacity.
St. Therese speaks of this in Chapter Two - "I once told you how astonished I was that God does not give equal glory in heaven to all His chosen. I was afraid they were not all equally happy. You made me bring Daddy's big tumbler and put it by the side of my tiny thimble. You filled both of them with water and asked me which was fuller. I told you they were both full to the brim and that it was impossible to put more water in them than they can hold. And so, Mother darling, you made me understand that in heaven God will give His chosen their fitting glory adn that the last will have no reason to envy the first. By such means, you made me understand the most sublime mysteries and gave my soul its essential food."
There in a 'thimble', so to speak, is one of the many small truths of the Little Way. We will be full to the brim when we reach heaven if only we fulfill our purpose from God. We each have our own vocations, missions and roles to fill in His salvation plan. Don't shy away from yours, don't think it is more than you can do - be brave in His grace and know you can do it!
But also - pray to made into a rain barrel!! I do not want to be content to be a thimble full of water but pray that I may be made into a rain barrel or a vast sea full of Him and only Him!