Boyfriend needs time to introduce me to his daughter, but only to one of them.?

We have only dated for 2 months but he seems quite serious about us. He has introduced me to the older daughter (16 yo) but not to the youngest (7). I like taking things slow and not rushing into 'family life'; however when he picked me up and my son was there I introduced them. We have been out for breakfast once and I am comfortable with these small things. He keeps the younger away from me. "Can we meet up a couple of hours Sunday before I go and pick up my daughter?" "I have my daughter on Sunday but I wonder whether we can go out on Saturday?" This begins to hurt. I talked to him about how I feel about this - and asked why it is ok to have met the older but he keeps so much the younger away from me.

He said he has discussed 'me' with ex and would like me to meet her before the child, so that she can be comfortable with the thing. He said that he is absolutely serious and has long term intentions with me and he wants to do things in the right way to ensure that I have the right place in his life with his children. He said that he is willing to come towards me and meet mid way if I feel uncomfortable. He asked me to have faith in him.

We are both in our 40s. He could get a hotter younger girl to play. But I wonder: is he lying? Or should I have faith? How long should I wait? When he says, let's meet 2 hours before I pick up the girl, should I do it, even if it makes me feel a bit of 'an affair' or just accept his wishes and see what he does in the next month or two?