Do I put my child's AGI somewhere since they filed a return for this year? First filing for child/dependent under 18

the child needs to fill out a separate tax return. 

how muvh did yhe child make?  If no tax withholding, the child may not have to file. 

If this is the first year your child is filing their own tax return, their prior-year AGI is 0.  If they attempted to e-file and the return was rejected with a rejection code of  IRS-IND-674-01, he/she will have to file by file.  The IRS doesn't allow e-filing for the first return of minors.  You should, however, take note of their AGI as they will need it to e-file next year.  

You do not need to report your child's AGI on your return.