My story was very similar to chesty's When we were just a couple, both earning, "marriage" didn't seem very important to me.
Roll on a few years and we'd moved in together, had baby no.1, still a great relationship. But me being the liberated young lady I was hadn't felt the need to get wed first. Over time, though, this started to feel important to me, having read a couple of stories about the legalities of having children when unmarried. And I started to feel slightly envious of the women whose partners had made this ultimate commitment to them (I know that this is not important to everyone, but it was starting to be to me). So I started dropping some heavy hints, not realising that most men are no good at taking hints.
Eventually one Xmas eve we were enjoying a glass of wine, and watching something on the tv where a couple got engaged. On the spur of the moment I said to him: Do you really not want to get married? I mean I would really like to have the same surname as the rest of you before dc1 starts school! We chatted about it - decided that we really should be married but we would only have a small ceremony (but I did have a fab dress!). Went shopping for the ring the day after Boxing Day and then announced it New Years eve.
So, there was no romantic proposal on one knee for me at the top of the Eiffel Tower, but I don't mind. And no big wedding either, but we've been married 6 years now and have a really good marriage.
I know personally of several women who have had to have 'the conversation' with their partner about marriage. And by 'the conversation' he has to know you mean business. I know one woman who had her bags packed and was ready to walk out the door - but she had no children yet, so it's a different situation to OP's. But she got her proposal.
OP - my advice to you is to have a serious conversation about it - only you can decide how much it bothers you. Do you want the romantic proposal and the big Wedding Day? Or the marriage? (I know you can have both). If you decide not to push the marriage thing, then please ensure that you put the necessary legalities in place (will/life insurance/next of kin etc) and make sure the dc will be financially secure should he leave/or if either of you die.