Can't Say the Letter T

Luke's language is coming along nicely.  His vocabulary is out of this world.  He knows most of his colors, some shapes, and a few animals.  He knows octopus and zebra, circle and triangle, and green, blue, and red as a few good examples. One thing Luke doesn't have a good grasp of is the letter T. Well saying the letter T anyway.  Anytime the letter T comes up in a word he says it silently. A good example is when he says the name of Thomas the Tank Engine it comes out as "Momas". Whenever we drive home we cross a bridge over water and a lagoon. When Luke sees the water he says "waber". After we drive past Luke says "bye bye waber".