The fact you have cracks in your new block wall would worry me..and with your wall not yet backfilled worries me a bit more because when a builder does backfill..the process of pushing the dirt against the wall with a bob-cat/backhoe etc. might widen the crack more because of the weight of the dirt being pushed against a new wall or the settling of it.What has the builder said to you about it? Has the city inspector been over to take a look at the cracks? Was the inspector there to OK the footing before the wall was built? Because if in the end of all this there IS a problem with the footing and the city passed it (I`m no lawyer) I assume that they and the builder can be found at fault. And I wouldn`t want to be told by a builder,inspector,engineer or anyone that "underpinning" the footing(if that is the problem) will be necessary.Not on a new home..no way.Because even if they try to underpin..there are no guarantees that the concrete they will use to underpin will also not drop,settle and eventually leave a gap between it and the footing which it was meant to support...follow me? And...in my 20+ years I have seen when builders have tried to fill block walls with concrete that it has actually weakened the wall! I wouldn`t be talked into that by anyone either.