Aryeh we are taught that when a child makes a brocho at the top of his voice and gets it wrong, Hashem smiles down on the child in the beauty of his innocent brocho.
Maybe you could look at it like this – the infant is participating in his own way with davening to Hashem
If you look it like this albeit it is not easy it will make you smile and cause you ease of mind at the innocence of the baby making gurgling noises instead of saying the words and as time goes by these noises will indeed become beautiful words that the baby will have learnt from all of you – what a z’chus.
Take a deep breath and enjoy the innocence of the child’s prayers as he/she davens with you.