A child under year of age is tough work I think. I don't have kids myself buy my sis and her boyfriend have 4 - the youngest has just turned 1. I see how little time they have for them and how much time they both spend working, seeing to the kids and keeping their homes running. I can so understand why and how friendships, social lives, time for each other and interests would disappear.
Really open communication is good. Seven years is a long time to be with somebody without feeling able to discuss fancying men and women. There must be so much that you and your husband have to find out about each other still.
I can totally understand you guys wanting to strengthen your marriage and become closer - it sounds as though it has been rather neglected over the years.
I don't get why you are choosing to do that through polyamory. Your post has talked a lot about you, your husband, your hopes for being closer to him and your fears about that not happening.
But - there is nothing in your post about what you or your husband have to offer to other partners. The other people you guys might date are living, sentient, caring, feeling human beings, not tools to strengthen a marriage that is proving to be hard going for the moment.
You say in your post that you have no friends and very little outside of home experiences. Why have you got no friends? Is it because you don't have anything to give to friendships? No time, money, energy? If that's the case - what makes you think that either of you would make a good partner for somebody else?
Why are you not going out much? Loads of my friends with babies take them to baby groups - breast feeding, weaning, yoga, water aerobics. There is much you can do with small children (I was on a camping holiday last year with 7 adults, 2 toddlers and about 15 dogs). If that's not your thing, you could be meeting friends for coffee.
My sis and her boyfriend take their kids (6, 4 year old twins and a 1 year old) skiing most weekends. The baby spent his first birthday on a mountain. They spend their weekends living with a large group of friends close to where they ski.
I love to spend time with my friends who are active, interesting parents. I'm not sure I'd see them as fun to be around if all they did was stay at home and be ground down by the demands made on them. I would support existing friends going through a tough time but certainly wouldn't start a new relationship with somebody who was struggling. Where would they find the time and energy to invest in getting to know me if they had no time or energy for their spouse or to maintain friendships?
You guys just don't sound like you have time or energy or the desire to be good partners and I wonder why you are choosing to consider polyamory?
I wish you luck and hope that you do find a way to strengthen your marriage.