First, to answer your initial question, No, you cannot be a christian and not believe in god, but you can be spiritual and not believe in god.
The Christian ethos "do unto others..."... you should know, it is not actually IN the bible. It is a saying that a lot of Christians have adopted, but is not actually not found in the bible anywhere. However, you do not need to be a christian or to read the bible for that matter in order to decide to live by that ethos. YOU can decide to live by it... all by yourself!
I feel your vision of teaching your children to be tolerant of other religions is a wonderful, open and loving way to go, and I commend you on that.
Before feeling bad about teaching the origins of Christmas and Easter, you should learn them. They date back farther than christianity as the christians actually adopted these dates and many of the traditions from the pagans in order to convert the pagans more easily to Christianity (an easier transition) at the time. If you study history you will find that religion, the use of it by powerful leaders, has been a major tool used to control the masses. This went on before christianity entered into the picture, and still happens rampantly today in every country, every religion.
You can believe in the teachings of Jesus, as these ideals existed before Jesus... he just assimilated them, and sold the package very well to the masses. At the time of Jesus, there were hundreds to thousands of others also professing to be prophets and trying to gain a following. It was kind of a fad at a time when people were politically torn and many were looking for direction and answers.... Answers that mankind has been searching for for ten of thousands of years, and each year, science answers more and more of those questions making religion more and more obsolete....hence the constant changing and reinterpretation of doctrines of religions worldwide.
I think you already have a lot of insight into this, and if you keep learning and asking questions, you will find that knowledge, science, and history are actually amazing, beautiful and complicated and can fill a thirst for knowledge that I believe you already have.
The reason man seems so much more special than other organisms is because we are simply more evolved. On a cellular level, our neurons are more advanced, and so we have more developed more mental capability and a higher conscience. How this evolved is a complicated, long term process involving natural selection, gene mutation, neuroscience, psychology, and others facets. But, the fascinating thing, is that this development can be broken down to a cellular level which evolve VERY slowly over time. Many types of humanoid species were fighting for existence in the past few million years. In the last 10,000 we won out over the last remaining competitor species...neanderthal. Evolution is an intricate, beautiful web of traits and genetics and is fascinating. You do not need to have a science degree to research these things and learn fascinating things that will keep you asking more and more questions.
That is the difference you will find between science and religion. Science encourages constant questioning and rethinking in order to come to the most reliable conclusions. Religion is the opposite.... it comes up with answers first, and then refuses to ask too many questions. People have a psychological defense mechanism to need these answers to explain unexplainable phenomena. Religions have explained these things to calm peoples' minds, but more and more it becomes obsolete as the answers are being discovered through furthered science.
If I were you, and what I have done, is to raise your children to be open, questioning beings. Research science and history for yourself and decide what is better.... for your children to live authentically and in reality, or to tell them a story that you, yourself doubt to be true. I encourage you to be brave and the more knowledge you obtain the more confident you will be.
As far as spiritual growth, there are many many ways to achieve this, and this can be researched, too. As far as christening your children.... I feel it is a personal decision and I have left it up to my children to decide for themselves about god, religion, and subsequently, baptism.
Baptism is one of many traditions used in many religions. Many of theses tradition are rooted in human psychology. Rituals help people solidify their beliefs and they incorporate their EMOTIONS, which is a huge huge factor in religion. Basically, appealing to your emotions is how they hook you.
Belief and faith are the opposite of reason, logic and science.
....and BTW, I greatly admire churches for their architecture, as well! I am an atheist, but this has come over a lifetime of contemplation and ultimately, an anthropology class made it undeniable for me. You CAN have morals and great values without religion. The myth that you cannot is something the religious will tell you to thwart you from thinking outside their box....