Enjoy them while you can. They're worth every bit of effort you put into them, and when they grow up, the things they remember about their younger years won't be the things you remember. Your life is changing, yes, but many of the things you did before, you can do with children...just at a slower pace. And all those things you *didn't* get to do as a kid yourself, well, this is the perfect excuse to try them! Nobody will say a word when you get up on the merry-go-round to hold your child on :-) They'll probably call you a "good dad".
...and kid hugs are the best!