My first child doesnt want our new baby?? :(

We have a 4 year old, and i am nearly 4 months pregnant, and he wants nothing to do with this baby. Tonight he came running with his hands out and shoved on my belly real hard and now im cramping and when we was explaining that he couldnt do that, and showed him a picture of a baby he got mad at slapped it out of our hands. What do i do? Im worried that if he hits my belly more like he did tonight that he might cause me to lose our 2nd child. He is my baby and always will be, nothing can or will ever change that, i love mommys little man ♡