My boy used to rush everything except the walk. I spent 3 years doing half halts at the trot and canter, and eventually got him going incredibly well, unless I actually pushed him. At one stage, when we were cantering I could have gotten off and walked faster that we were travelling. I used circles with him and half halts, he was still a bit full of himself for a while when we were out and about, but he realised that the minute I put my bum back in the saddle and sat into him that he was going to be told to slow down.
God I miss that boy..............actually, I miss riding. Its killing me not riding at the moment :(
Good luck with your baby!