The average child DOES love his/her parents unconditionally. That is because in the earlier years, the average child is very vulnerable physically, emotionally, mentally, psychologically, & even psychically. He/she see his/her parents as all encompassing & perfect. He/she is also highly cognizant of the point that he/she must depend upon his/her parents for his/her very survival & growth as there is no other choice but to love his/her parents unconditionally.
Children receive messages that they are to love their parents unconditionally. These messages are not only from parents themselves, societal & religious messages strongly inculcate children that they MUST honor(love, respect) their parents above all else & not to do so is considered to be an affront against a preordained order. Children in their early formative stages are not knowledgeable enough to not to see their parents more negative aspects & shortcomings so they are quite accepting of their parents, foibles & all.
Children have the habit of rationalizing their parents, even in the most horrendous, harsh, & abysmal conditions. They strongly contend that if negative circumstances occur, it is not their parents' fault. In fact, they rationalize, even justify, such environments as a natural fact/part of living. How many adults from dysfunctional or extremely negative familial backgrounds state that they grew up in such backgrounds, proclaiming look "how well" they turned out. They refused to see the negativity in their parents & environment, asserting that all is well although it was quite the opposite.
Children want everything to be alright, even the negatives. They will explain away any quality of their parents that is not possible, always portraying their parents in the most positive light. They do not want to think of their parents as less than their particular ideal, even though the parents can be classified as very negative people.