Can I amend my tax return which I filed in January and add kids after I got stimulus fund money only for myself?

I filed my tax return in January. At that time my ex husband and I had an agreement that he will file our kids on his tax return. He still didn't file it and he does not mind if I can show them in my return, since our kids live both with him and with me equally.

Yesterday I received a refund from stimulus fund at amount of $1200. I wanted to amend my tax return and add my 2 kids to get a stimulus for them too. 

Will I get the stimulus money for my kids after amending my tax return? 

What do you recommend me to do?