When my kids were that small we would travel with one of their car seats for the plane. The car seat is restrained by the plane’s seat belt and then your child is nestled snuggly in their own car seat.

The benefits are that your kid is then in an environment they are familiar with and they can’t just wiggle out. The downside is that you now have to lug around a car seat in the terminal. Ours got stuck in an X-ray machine once. That was fun.

I assume that’s still possible, it’s been a while since we had to travel like that.