As someone with a 5 year old girl and a 2 year oldboy, I don't know whether to offer congratulations or condolences
-just kidding. Welcome aboard the greatest adventure of your life, seriously!
Don't let anyone tell you that it's time to hang up the helmet for good; I ride more now than before my kids were born (stress relief, eh?).
PS, I'm with you on the planning the kid's first 50. I got my daughter riding a bicycle this summer so that we can build up enough skill to go for it in the spring, hopefully.