we have two shires that are big puppy dogs also, so much so that my almost 3 year old can lead them (they tend to just follow him as he is known as the bringer of cookies). They're ever so gentle , and huff along behind them with their noses on his shoulders begging for treats (a bad habit I know , but they're not nippy at all, my boy likes to sit on the tree stump and hold the bucket while they eat - he likes the huff huff noises they make haha)
Manners (at least to me) are a biggy as they are so much bigger than I , and as I am quite unwell I am unable to go tugging on the end of a lead rope , and it would be very bad for me if they were to push me around. As such we do alot of work on their manners , and if they do start getting wily I will not hesitate to pop them on the shoulder.
But for the most part they are gentlemen - their one bad trait is tending to 'lean' on the farrier, or when you pick their feet, or to lick your backside as they know I usually have a carrot in my back pocket , they are notorious pick pockets our two!.
A shire leaning on you while your doing their feet is not pleasent!
TBH I have more problems with fatty shetland pony than I do them!