I used to do a 15 miles one way commute with a newborn (at home) three or four days a week. I started commuting before the kid with a hybrid and then switched to a 30+ pound tourer (exhibit B). I found no appreciable time difference between the two. I now only commute 7-11 miles each way every day with a daycare run most days.
I also recently got a race bike (18-19 pounds, exhibit A) and I would say my commute times have improved at most 10%, so six minutes in a hour. That is following most traffic rules (using Idaho stops at stop signs) and regular city traffic; as a parent I am a huge proponent of self-preservation and take extra care. According to strava my average speeds are: on the daycare run is 22 km/h, normal without kid and seat is 24 km/h and on the race bike barely 26km/h.
So to me it is not worth the extra money for a race bike, it was a great craigslist find and birthday present from my wife to get me into racing. I like that with my LHT I can go on group rides with it and keep up with the B group without big long climbs. If I wanted to race it I need about eight minutes to remove my racks and fenders (probably 15 to reinstall). I would feel completely comfortable doing my initial triathlons on it. But I would scour craigslist for a nice bike to start triathlons on; take your time and a good deal will pop up.
I found that the cycling was crucial for my family. It takes me nearly the same amount of time to ride as it does to drive. Riding makes me happy and I have energy when I get home. Driving makes me sloth-like and grumpy when I get home. Last thing you want to be is grumpy when you get home. So cycling was crucial for mental health, physical health and family cohesion. If I didn’t ride I would have to take an extra hour to go to the pool or out for a run. So a double family time loss.
So in summation: Go get ‘em tiger!
Exhibit A:
Exhibit B: