So I have 3 dependants under 18 and it says I'm only getting 1090 back! How come its not including what I should get back from them being dependants?

Under the new tax law if your children are less than 17 years old you receive as a credit against Federal Tax owed a possible Child Tax Credit of $2,000 per child.  Since you have 3 children you may possibly qualify for a credit of $6,000 to reduce Federal Tax you owe.  Child Tax Credit is a non-Refundable credit and only reduces what you owe for Federal Taxes to zero.

The amount of Federal Tax you owe is on Line 16 of your form 1040.  If you do not owe any Federal Tax then you do not receive any Child Tax Credit.  If you owe $2,500 in Federal tax you only receive Child Tax Credit for $2,500.

Link to more information about Child Tax Credit