a few weeks ago john started saying something that sounded like "mice" all the time and we couldn't figure out what in the world he was talking about (which, of course, was infuriating to him and would usually end in a screaming fit). finally, we realized he would use it in a possessive sort of way, indicating that something belonged to him. it dawned on us one day when michael said that something was "daddy's" and john firmly corrected him, saying "no, mice!" that's when we realized he was duplicating his daddy and stating a possessive "my's". and although it's incorrect, i'm still astounded that little kids can be so brilliant to apply grammatical rules to their words like that.
seriously, i don't think it's possible to not enjoy watching kids grow up.