Sounds to me like the OP doesn’t rate his chances and is already making excuses!
The trick is to make it look like you’re not making an effort – stealth mode.
Maybe put in some practice sprints a few weeks leading up to the day. In secret of course – don’t even let the wife know as women talk and you don’t want this getting back to the playground. Obviously, if you have to Strava them to monitor your training – tick the private box.
Last year, I turned up in a footie shirt and some craghopper shorts with some Asics on but not proper running shoes. The clothing suggested casual but thought had gone into it – zipped pockets and light footwear with a semi fitted top.
You’re aiming for mid pack really so you look like you’re not competitive but still beat any of the dads who your kid is really friends with. You need to assert dominance over those parents that you see on a regular basis. You’ll always gonna have those “teenage pregnancy” dads of 20-22 who you will never beat so don’t get too hung up on it…..
Our kid’s school is fairly big so there were 3 races for dads. I milled around to get into a decent race where I was against my boy’s best friend’s dad and a few fat knackers. Got out the blocks fairly quickly and came through with a faster finish where others were fading. Ended up finishing 5th out of about 11 beating my main target by a couple of places.
Dominance asserted and the boy had a few bragging rights in the playground. Job done.