Did you enter them as dependents? Did you enter their Social Security numbers? Did you enter your own income that you earned from working? Is there a specific credit you expected to get that you are not seeing ?
Your child-related credits are affected in a big way by how much income you earned by working. If you only earned a small amount of money in 2019 then you will not get a big refund.
Make very sure that you have entered every cent of income you received in 2019 in Federal>Wages and Income. Every 2019 W-2 and every 2019 1099 you received have to be entered on the same tax return.
Your earned income credit is based on how much you earned by working. There is a link below that you can use to see how much EIC you should be getting for the number of children you claimed under your filing status--Single, Head of Household or Married Filing Jointly. (If you file married filing separately you cannot get EIC)
The child tax credit is a credit of UP to $2000, but not everyone gets the full amount. First the credit is applied to any tax you owe. Then the "refundable" amount of up to $1400 is calculated. Look at box 1 of your W-2. Subtract $2500 from that. Then take that number and multiply by 15%. That is your refundable amount --or "additional child tax credit" amount. If you did not earn at least $2500 you cannot get any child tax credit at all.
Look at your 2019 Form 1040 to see the child-related credits you received
Child Tax Credit line 13a
Credit for Other Dependents line 13a
Earned Income Credit line 18a
Additional Child Tax Credit line 18b
Child and Dependent Care Credit line 18d