The only advice I can give is to stop it as soon as you see it and explain that bub might get hurt. DD1 started to do it too but luckily I discouraged it enough where she got over it and doesn't try anymore. It didn't take long. DD2 is now at the age where she doesn't like it and will push DD1 away.
Our issue is that Brendan doesn't have that understanding, so stopping him from doing it becomes quite an issue, for him and us.

I might just have to keep Tristan with me all the time now... which again gets complicated with toilet breaks ect.