As a kindergarten teacher, you learn a lot about speech development. It is frustrating at that age to have speech delays that are considered developmentally appropriate. The /th/ sounds are not typically mastered until age 8... but it's hard to explain that to a parent who is worried because their child says "tink" instead of "think".
Being on the other end of the spectrum I find it interesting that doctors do not explain this to parents right in the beginning of children's speech development. Children are not expected to "master" any sounds until typically 3 years of age. Also many common speech "errors" are not real errors at all in a 1 or 2 year old, but just typical developmental stepping stones.
At this time, Blake says about 20 words, but many of the words he says he drops the beginning sounds ("ilk" for milk). This makes it hard for some to understand what he is saying as "real words". The big thing parents need to understand (and should be stressed by doctors in my opinion) is at the this age children are beginning to learn that words are used for communication, and if you can understand what your child is trying to tell you and uses the word correctly... then it is a mastered word.
Speech development, like all other development at this age, happens when the child is ready. Parents need to watch out for falling into the "Oh no my child isn't doing it as fast as that child" trap. I feel that if pediatricians helped parents gain a better understanding of speech development then parents would have less to panic about in this area!
Interesting article on speech development if you are interested in the typical ages and stages of articulation development: http://members.tripod.com/Caroline_Bowen/acquisition.html
here's a list of Blake's more common words / phrases:
Momma (and many forms of that)
Daddy (and other forms of that)
Abbu (for Abby)
uck (truck or duck depending on the situation)
ank you (thank you)
all one (all done)
ead it (read it)
I did it
ove oo (love you)