It seems that this is perhaps a rather cynical view of the "infant" stage of life. Yes, as any parent could tell you, there is certainly a large amount of "Mewling and puking" but at the same time to suggest that this is all that there is to this stage is a travesty. Speaking as a parent, every stage of parenthood is incredibly precious and at the same time challening.
"At first the infant,
Mewling and puking in the nurse's arms."
How do I feel about this infant, or the way Jacques discusses this stage of life? I suppose I have mixed feelings, personally. I remember both of my kids being mewling and puking, but I loved and adored them through it all. Jacques, however, is cynical and showing it through this soliloquy on the seven stages of man. He is sarcastic about each stage of life, and I find the saddest one of all to be his description of #7:
"Last scene of all,
That ends this strange eventful history,
Is second childishness and mere oblivion,
Sans teeth, sans eyes, sans taste, sans everything."