It may mean he feels used. Like all he is there for is to watch your children. If he has no job, then tell him that IS his contribution to the household. If he has a job, he really is not their father and if he is always being left with them and you don't hire a sitter so you two can spend time alone... he feels he is your babysitter and little else. Not sure if this is the case but couples often get so caught up in day to day life, they forget to spend time looking in each others eyes and really understanding each other. Not sure your case...just throwing spit balls.
He feels like their too much o a burden and that he shouldn't have to be constantly babysitting or picking them up from things. Pretty selfish but its how guys are when they date people with kids from past relationships
Sounds like it means he needs a job. Or to work more hours or to have considered all of this b4 moving in or moving you in. But all in all if he works, and works enough hours, then it likely means he doesn't see your kids as his kids or his responsibility which means he's not likely to marry you.
Well, at least he's honest. This is one reason why it's best to stay with the father of your children bc otherwise things get messed up. Is he kind and reasonable with the children? Take that into account. So, he's feeling used, but maybe he should be at work or what?
Sounds like he's either feeling unappreciated as mentioned before or he's just simply missing the time with you. Raising multiple kids is a busy chore and sadly usually the parents/adults fall into a routine that solely involves the kids lives and leaves little time for each other. Sounds like its time for a date night.