Vivacia - You can fuck off. Seriously. This is an annon forum and women should have the freedom to talk openly to their peers, without shame, without judgement from Judgey Mc Judgersons like you.
To the OP - I think there are a few issues here.
- You've only had sex with one person, and it's natural to wonder what it's like with others
- You've been talking to, or listening to girlfriends talking about sex and comparing your sex life to their experiences
- A lack of communication between you and your partner.
For the first one, there isn't really much you can do about it. I think it's okay to wonder about in a philosophical sort of way, but if you are happy overall in your relationship, then it just isn't worth worrying about. It's like thinking "maybe life is so much better in the US. Maybe it would be amazing". But at the end of the day, your whole live is in London and you're happy there, and you aren't moving. Okay that's a bad example, bear with me it's late here. But hopefully you get my point.
On the second one - take what you hear with a rather large pinch of salt. Women talking about more casual encounters will naturally tend to exaggerate what happened in order to tell a good tale. Women in relationships will normally only focus on the good (if happy) or the bad (if heading towards a break up). They generally won't tell you about the weird awkward things that happened, that time they had to spend 15 minutes looking for a condom then both just fell asleep instead...etc.
Television is the worst for this. Like that god awful show Sex and the City!
Aside from this, having married this man already, it shouldn't matter what size he is. There are lots of ways to work around that if it were the case. But that said, five inches is a perfectly normal size. It's not massive, but I would in no way class it as "tiny". So hopefully that puts your mind at rest a little.
You mention he "feels" narrow, and....I hate to link these, but you mention that you have children. Did you give birth vaginally? And if so, did you work on your kegels after the births? Obviously things down there get wider after pushing small humans out of it, so that could be an issue as well, rather than purely him.
People have given you some good ideas here, and hopefully you can discuss them with your partner. The trick is not to be a complete bitch when talking about it. Think about how you would want to be approached if he had a problem with you. You do it gently, and from a positive angle. Eg, I love this, but I'm not so keen on that. I would love to try this - would do you think?
Also, just as an aside, speak to your partner before you unveil some purple giant sex toy to him. Many men are very uncomfortable with the idea of sex toys, especially when used for penetration. You should work out his views on them first rather than putting him in an uncomfortable situation. You can always start out with the smaller non penetrative ones and see how you both get on with them.