You have to write them down...you really do. You absolutely will forget a lot of those cute things your kids say when they are trying to figure out the language. There will be occasional events that trigger a memory, and some memories will stay strong, but wouldn't a book full of those cute little words be wonderful? I am sure I have forgotten a lot more than I have remembered.
My two daughters are different as night and day. I have always said I received the best of two different worlds in their arrivals. They are grown now, but some of the words they coined are with us still, or at least with me. Both talked early, and learned the language quickly, with fun things along the way.
DD1, when learning the parts of the body, said "elbow" and then pointed to her leg joint and said "kneebow". It made sense to her, and I must say I agree. FeeVee was the designation for the television, and compound words were reversed: widesalk, sindowill, and flutterby were the favorites. She was convinced that the thing that went around her neck at mealtime was called a bibon - isn't it just obvious why? Have(with a long a) was a verb, as in, "Mommy, I'm being as have as I can!"
DD2 preferred belbow as her arm joint reference, but loved the y sound. Yadeerow was her word for radio and we still call the little round candy covered chocolates Yem and Ms. Anywhere you went to get something was a store: grocery store, clothing store, money store(bank) and dinner store(restaurant).
Kids have such a great view of the world and often make more sense than do we adults. It is such a joy to watch them experience learning. I am now blessed with two grandchildren and am witnessing that fun all over again.
Please share your kid word memories. They are smile makers, and we can never have enough smiles!
Peace and light