https://codes.iccsafe.org/public/document/IRC2018/chapter-3-building-planning

But, there is no good excuse for interior stair treads to be anything but level.

Normal is level, abnormal is not, Are they[stairs]temporary ? or permament. All treads and risers should be the same.

That would be my question to the builder, not here. How can even help. Often the treads are temporary in the bulding phase so ask.

If it is noticeable, something's wrong.

Sometimes when they put the stairs in, they put temporary blocks under them so if your flooring is going to be tile or hardwood, they would slip a few pieces of flooring or 3/4" scraps of plywood to keep the stairs up. If they don't secure this temp pieces to plywood, they get kicked out or when the house is being swept sometimes sweep them out so the stairs will drop down and get out of level. Just bring it to your builder's attention and he will correct the issue, I'm sure they will not leave them that way (hopefully).

When your builder finds a big 'ole red tag on his stairs, he'll have no luck explaining to inspection that they are "too picky", believe me.

put a small level on them and take a picture showing the gap at the front of the stair tread. Even with a ruler there showing how much slope. Provide this to your builder as part of your punch list / home warranty.

I am sorry you are going through this and worried about your kids hurting themselves.

If it's noticeable to you on "feel", and you feel uncomfortable walking on them - there is no way you are being 'too picky'. I freaking hate that - somehow the defect here is you and not the sloppy construction? Takes a lot of nerve....

bellburgmaggie is right. I suggest that when purchasing a new home you have it inspected twice: First time before sheetrock, second time before closing. Most inspectors will make a fair arrangement for this.

Your tread should not slope more than 2% per R3.11.7.7 of the International Residential Code. On a standard tread that should be less than 1/4" Jannicone's method will let you know if your stairs are to code. I would also check the stairs for level across the width of the stair where you're noticing the awkwardness.