Anyone with small children ?

My oldest is 14 months . He is still very much a baby himself . He isn't capable of understanding his actions MOST of the time . He is very rough , like little boys should be . He also can be very loving when he wants to be . He still wants mommy to hold him all the time, it's getting very exhausting .. Not to mention he's very rough when I'm holding him . He's kneed me or kicked me in the stomach a few times .. Not very hard but enough to startle me for a few minutes . I tell him no and it hurts of course , but he doesn't understand why I'm telling him no . He just looks at me ! I don't know what to do about it , I know the baby is we'll protected and is still very low at this point .. But I can already feel the top of my uterus and I now further along it can cause issues . Any tips on how I can teach him that there is a baby in there . We talk about the baby to him , I've even introduced a baby doll into the nursing secessions because if the lord is willing I plan on tandem nursing ! He's just not capable of understanding what is going on ...