I used to use a used breast pad to cover DS1s willy when changing him, the heaviness kept the willy down even with the force of weeing (and there was even occasionally enough breast pad left not saturated with milk, to absorb the wee.
I did take 6 nappy changes to work it out tho......after being so used to changing girls, (I also had my first boy after 3 girls) I never even expected the boys bits. He literally got me soaked on every nappy change in the first day!
oh, and he had erections from day dot too.
that said, I DS2 never wee'd on me, and he had fewer than 5 erections in all his times in nappies, that I saw at least.
otherwise, boy babies are much like girls, until they start to move, and then both (of mine) were ball obsessed.........DS1 still is, the real kind and the flesh kind.
I do find them more physical.....they need daily excersise. my girls were happy to play babies and tea sets and colour in all day. My boys by contrast go around bashing and kicking and climbing and shouting and wrestling..................yada yada yada.....
they are fabulous tho, I would not be without them. and they are very loving to their old mum