Will my 2020 tax return be amended to reflect the new covid relief tax laws. Including child credits and stimulous checks

When it comes to the child tax credit increase you will be able to get it disbursed via monthly payments starting in July or you can claim it on next years return for a lump sum

Please see this answer from HalAl.

The new (expanded) Child tax credit ($3000; $3600 for kids under 6) is effective for 2021. There is a provision for advanced monthly payments  being made in 2021. The payments will come from the IRS, similar to the stimulus payments. The details of how and when are yet to be worked out, but  starting in July has been mentioned.

Getting the expanded child tax credit has nothing to do with filing your 2020 tax return. Whether you already filed, file now or file later, the additional money will not be part of your 2020 tax refund.

Please see this Link for more information. 

Please see this LINK2 for more information.