What is the 2018 Standard for a single mom head of household with three child dependents?

For tax year 2018 (prepared next year) the standard deduction amounts will increase to$12,000 for individuals, $18,000 for heads of household, and $24,000 for married couples filing jointly and surviving spouses. 

For tax year 2017 (prepared this year) the standard deduction for single taxpayers and married couples filing separately is $6,350; for married couples filing jointly, the standard deduction is $12,700; and for heads of households, the standard deduction is $9,350.

plus a small additional amount if age 65+
Starting in 2018, there are no more Personal Exemptions, You would have received a deduction of 4 x 4,050 = $16,200 in 2017 for these.