The correct answer is B. have been.
The sentence is in the present perfect tense, which is used to talk about things that started in the past and continue to the present. In this case, the speaker is saying that they have been fond of football since their childhood. This means that they have always liked football, and they still like it now.
The other options are not correct because they do not express the idea that the speaker has been fond of football for a long time. Option A, am, is in the present tense, which would be used to talk about something that is true now. Option C, has been, is in the simple past tense, which would be used to talk about something that happened in the past. Option D, will be, is in the future tense, which would be used to talk about something that will happen in the future.
In conclusion, the correct answer is B. have been. This is because the sentence is in the present perfect tense, which is used to talk about things that started in the past and continue to the present. In this case, the speaker is saying that they have been fond of football since their childhood. This means that they have always liked football, and they still like it now.