Will try and keep it brief.
I have one DC with DH who has 2 children from a previous relationship as well (DSD 11 and DSS 8). I have been with DH for 4 years.
We argued about something unrelated a few days ago and he brought up that I do things alone with our DC and it's not nice for DSC to "think I just want to spend time with our DC".
We argued about that for a little while as I think that's ridiculous. Of course I want to spend time with my child sometimes, I'm not going to pretend to him otherwise and I don't think it makes me a bad person.
Of course I'd never outwardly say to DSC "I don't want to spend time with you today" but yes I do take DC out on our own sometimes. They are much younger so not loads to do that all DC would like and I think it's nice for us to have time together occasionally.
We also do things as a whole family too.
DSC live with us 50:50 so sometimes they are here when me and DC go out but not loads and they have never said or even seemed to remotely care.
I suspect DH is just saying it to get at me.
But AIBU to think it's ridiculous and that obviously I can (and also am allowed to want to as well!) go out with my DC alone sometimes!