My ds (4.5) spoke very clearly and in complete sentences relatively early and he has a fantastic vocabulary. However, when he got to 3 (ish) he began to over-generalise many irregualr, past-tense verbs that he had previously known, eg 'went' suddenly became 'goed' etc. I thought that this was a normal phase that indicated that he had picked up on the 'rule', such as it is, and did not ever consider correcting him. I would usually repeat the sentence, or add to it in some way myself with a correct version of the verb in it but I didn't do this in a critical way and never got him to repeat the correct version or anything like that.
However, recently I have become aware that he seems to be doing it more and is showing no signs of stopping and I just wondered if gentle correction was appropriate now or not.
Similarly, I have noticed that he appears to be inventing quite complex words as part of his play - they sound similar to real words but are nonsense. Eg he will say, "I'll get my tea-set out so my toys can espondualte their food," or something - it sounds a bit like he is trying to copy real words he is vaguely aware of to make his game real - does that seem possible? Should I be trying to work out what he means? Do other dc do this? I am sure they do - just wanted to hear other's experiences.
I'm sure I am over-thinking this terribly 
but I just want some reassurance that I am right not to correct him in these instances.