One of the reasons I left ex DP was that he wasn't very involved with the DC. They didn't listen to him, were rude, bossy and demanding to him, they'd hit him and tell him they didn't like him. I would tell them off but he would carry on letting them do as they liked so eventually I became tired of always being the bad guy.
He doesn't want to see them away from me or my home but when he's here, he's still letting them behave badly towards him. Tonight, for example, our four year asked me to take her shoes off for her. Ex DP and I were carrying shopping in and I told her she's quite capable of doing it. As ex DP passed her she kicked him and said to take her shoes off for her now, and he did 
At dinner, our almost 3 year old was climbing all over him, repeatedly getting down from the table, throwing food - things he would never do if ex DP wasn't here. Ex DP just kept watching him do it then trying to pick him up to put him at the table, DS was hitting him and ex DP said nothing.
When he is here, they make a huge mess knowing he'll tidy it which is against house rules of you make the mess, you tidy it. He hand fed both of them dinner when they're more than capable and knowing they'll likely try and demand the same from me tomorrow when he isn't here - therefore leaving me to be the bad guy yet again. We went to the park after tea and I was carrying our new born. DS refused to get in the push chair for ex DP and refused to hold hands for roads, hit him several times and ran into the road to get away from ex DP to me. Ex DP said and did nothing and has no control whatsoever.
AIBU to think he's undermining me by continuing to not actually parent?