Will not go in gear when at a complete stop

Early mornings when I start my van sometimes will go in reverse, but main issue is when I put it in drive from reverse it sounds like it is in neutral. Mainly when I stop at a stop sign it won't go in gear. It just raises the rpm's and then kicks hard into gear. But if I let it kick into gear on its on it takes up to five minutes. Very dangerous when I go to pull out of the store and it just randomly decides to not go in gear and I am stuck in the oncoming traffic and my two year old is with me. But if I drive it long enough it will not do any of that and makes me look dumbfounded when I tell someone about it. It is almost like it needs to warm up first. But going up hills it does it and rolls backwards, then kicks in gear! When I start to push on the brake I feel a kick, if I feel that kick I know when I stop it will go. If no kick. It does not go. Please help. It is my only transportation for my son to get back and forth to physical therapy and occupational therapy and his brain surgeon.