My BIL & SIL are only in their late teens & early 20's, but I know it was hard for them when ex & I split. Hard for me too, to leave them They were 4 & 7 when I first met them.
I love them & stayed with his family for 2 weeks when I went home. Nothing will change my relationship with them. SIL, MIL & I text all the time. It might be different given that there are kids involved, & that they are with me, but I have more to do with them than ex. He's an hour away, I'm on the other side of the country...