It sounds blasé, but you just have to commit the time. I started my fitness journey right after we had our second. Getting up at 5am to workout when you have a 4 month old is a challenge. Once we got through the newborn phase and he was sleeping all night, it was that much easier.
You also may need to give up other hobbies. There is enough time to workout during the day if you’re committed. But maybe you don’t have time to watch every sports game, or have to cut back screen time, or whatever. You also need buy-in from your spouse so she knows why you’re getting up early and need to get to bed at a decent hour. I’ve had to give up reading books during this phase of life. Just not enough time to read and get to bed early enough. I just prioritized fitness over that particular hobby.
For me, with kids, I have to do my workout before everyone wakes up. If I try to wait until the end of the day either someone’s having a meltdown or I’m exhausted. It’s tough when my alarm clock goes off, the house is cold, and everyone is still sleeping, but once you build that habit, it will get easier. Mornings may not be your time, you have to determine that. Just find the time that works best and stick to it. Consistency is key.
Hell, I’m sitting here about to go to the gym at 4:45am when it’s 20 below outside. I actually look forward to days like today because it means fewer people at the gym. Pre-2019 me would not do this in a million years. Even getting up at 6am to workout before then would be a non-starter for the old me.