@rickram It's going to be fine! A huge change, but in two years I'm sure you'll look back on this very positively.
Since your wife only had 9 months between birth and conception instead of the recommended 18 minimum, her recovery this time is likely going to take longer and she's likely going to be much more tired. This means you'll probably have to do 100% of the toddler stuff anyway, in addition to a big chunk of the newborn stuff. So I don't think your relationship with the toddler will change that much.
Since your wife only had 9 months between birth and conception instead of the recommended 18 minimum, her recovery this time is likely going to take longer and she's likely going to be much more tired. This means you'll probably have to do 100% of the toddler stuff anyway, in addition to a big chunk of the newborn stuff. So I don't think your relationship with the toddler will change that much.