I have questions - does your wife prepare your meals? Does she clean the house? Does she ensure the house runs well? If you already have someone who's doing all that then maybe i can lean a bit towards you. Even then, i do not see anything wrong in getting extra help. Mothers are sleep deprived, going through hormonal changes, struggling to still make sense of her day and listen to you. So Akinseye, if she needs a nanny for her sanity, please please give her one.
It's like saying, why do you need a driver when you can drive to work - Lagos will run you mad sometimes and you can use your free hands to do something worthwhile.