If i gave my baby pear after steaming and boiling so become smooth does it loss its nutritional value?

Not likely: When canned fruits were studied, it was found that many of them actually had more nutrients than the fresh products (which had actually been in storage or in transit for awhile before reaching the consumers). Although this does not answer your question directly, it does show that cooking has little effects.

Cooking food: In general, any cooking depletes food of some nutrients. On the other hand, it makes other nutrients more accessible by making the food more digestible. It can also denature irritants in food that can cause stomach upset and kill harmful bacteria. This is about cooking in food in general. Perhaps another contributor has something to say about pears in particular.