Babies Babies & more Babies ❤️💙

Okay. My ex and I have been separated for over a year now. We both have moved on to better things. Together him and I have 2 beautiful babies. Now my current boyfriend and I have been together for 4 months but knew each other all throughout high school where we graduated in 2013. We are in love. Very much in love at that. But here recently I have been wanting another baby.... The last time me and my SO talked about it, he said we should wait a little bit. Mind you my first 2 kids, live with their dad and his girlfriend because they are very attached to them. This morning me and my SO had sex and for only the 3rd time ever, he came inside of me.... His immediate reaction was "that will never happen again".... I really want to tell him that I'm ready for another baby, but I'm so scared of his reply.... 
Should I even say anything? If so, how should I say it?