Not only 3+ dependents, but single parents as well. The "head of household" status goes away and is simply "single" if the plan passes.
Reagan didn't start by simplifying - in 1981 he lowered taxes, just as George W Bush did in 2001. Next year with Republican control (except filibuster) of Congress and a Republican President, history suggests taxes will be lowered. Of course, while we rejoice $9,400 less in taxed income, companies will be celebrating their taxes getting cut in half (35% to 15%, per campaign promise). It might be equally interesting not just to speculate about the tax situation next year, but how the massive reduction in government income will impact people's lives.