The Recovery Rebate Credit is on line 30. Nothing to do with the Child Tax Credit on line 28. Oh, you have 4200 on line 30? That is the amount for 3 persons (1400x3). And you didn't get any of the 3rd stimulus that came out last March 2021. Like I said above double check your bank statements. They IRS shows they already sent it to you.
If you didn't get the 3rd Stimulus check but the IRS shows they sent it to you then request a trace for a missing third Stimulus payment
https://www.irs.gov/newsroom/questions-and-answers-about-the-third-economic-impact-payment-topic-j-p...
