The first one is an unreal past conditional (3rd conditional) and it describes something in the past that didn't happen or wasn't true. If I had had a normal childhood ... - I'm an adult now and I didn't have a normal childhood. if + past perfect form The second one is an unreal present conditional (2nd conditional) an it describes something that isn't true at the moment. If I had a normal childhood ... - I'm still a child and my childhood isn't normal. if + past simple form You could also do a possible future conditional (1st conditional). If the baby has a normal child hood ... - Maybe it will, maybe it won't. if + present simple form

Suppose we don't know if Tom's childhood was normal. We could then say "If Tom's childhood was normal, he will now be a well behaved adult." However, if we know that Tom's childhood was not normal, we would use subjunctive mood: "If Tom's childhood were normal, he would now be a well behaved adult." That is because the verb "to be" has its own special subjunctive form: "were". No other verb has such a special form. For all other verbs, the subjunctive mood looks exactly like the past tense. This lack creates ambiguity. However, proper use of modal verbs can help correct this flaw. Let's look at these three sentences: (1) "If Tom had a normal childhood, he will be a well behaved adult." (2) "If Tom had a normal childhood, he would be a well behaved adult." (3) "If Tom had had a normal childhood, he would be a well behaved adult." The word "if" means all three sentences say it is possible that Tom did not have a normal childhood. However, (2) says it is more likely that it was not normal, and (3) makes it almost certain that it was not normal. The difference between #1 and #2 is in the words "will" and "would". "Will" expresses certainty (not future tense), while "would" expresses doubt, raising the probability that the childhood was not normal. However, it still MIGHT have been normal. #3, by saying "had" twice, makes it almost certain that the childhood was not normal. We know the first "had" to be in subjunctive mood. How do we know that? Because there is no other plausible reason for saying the word twice. Past Perfect makes no sense in this context. The second "had" can only be there to make the situation hypothetical.