My grandchildren sometimes kicked during diaper changes at that age. My granddaughter usually thought it was funny. My learning disabled grandson kicked really hard. Sometimess it was for fun. Other times he seemed angry.
With both of them I moved to the side so that they couldn't reach me, help my hand on their tummy so they wouldn't roll away and say something to the point of I don't think this is funny. stop kicking so can get you diaper changed and have some fun. And then we'd play, usually in a physical way to work off the energy. One game is I'm gonna get you as I'd reach in their direction and they'd say I'm gonna get you and reach out in my direction.
sometimes, I'd play a game with them by pushing back on the feet and she'd kick into my hands and we would both be laughing. Then I'd say lets get this diaper changed so we can do something else fun. This didn't work with my grandson.
Sometimes, I'd say oooo! that hurts! Please stop. And my granddaughter would stop after a few more tentative kicks during which I'd hold a foot and repeat please stop.
That one rarely worked with my grandson. After that we found that he has speech apraxia and possibly has an autism spectrum disorder. He still doesn't realize how hard he hits. He does this hard hitting even when he's not mad. He also joyfully runs helter skelter into me with enoubh force that I would fall down if I didn't brace myself. We are still working on stopping that. He likes for other kids to run hard into him.` I try to prevent the losing balance part for me by reaching him before he reaches me.
At 18 months stopping him by moving away from his feet frequently didn't work. It was just too much fun for him. At some point he didn't even like to lay down for diaper changes. His mother switched him to pull ups so that he could stand to have his diaper changed. That was OK for him.