I responded to your other post.
A NegAm loan (or a Pay Option ARM) usually offers 4 payment options: The lowest is the one that causes deferred interest, meaning your total loan balance is higher after you make the payment. The next payment is the Interest Only option, meaning you pay only the interest due on your loan and the balance remains the same. The other two options are 30 year amortized and 15 year amortized, meaning the loan will be paid in full if you make the same payment for 30 or 15 years.
What I suggest is a 40 year loan with the first 10 years being interest only. Fannie Mae offers this loan with her MyCommunity program. Yes its expensive in the long run, but by then your child will be older and you will be earning a higher income with you and your wife both working. Also, this is a conventional, conforming loan and has no pre-payment penalty. Can you afford the payment? That depends on the cost of your insurance and taxes and of course your ability to sell real estate.