Claiming child benefit while outside the UK

I'm British and my husband is Mexican. We just got married. We have a 3 year old child together. We have been living between the UK and Mexico since we have been together. (4years) he is allowed 6 month tourist waiver upon entry in the UK.

Before my son was born I claimed I was a single mother because I was desperate for money to live off and to buy things for the baby, also my partner had no money to contribute anyway, not able to work and my family could only provide so much. After a couple of months I started working and paying taxes but I still recieved child benefit for my son. I have never cancelled this benefit and we have been spending 6months to one year out the country at a time. I didn't realise until recently you are only allowed to spend 2 months out of the UK to receive child benefit. This money was a lifesaver for us while living in a low income country.

I am returning to the UK later this year to find work that meets income requirements and start his visa process. (Spouse Visa)

Since I have to prove we have been together throughout this whole time will they look into the child benefit I recieved for my son and cross reference it with me being out the country and in a relationship?

will this affect negatively against our spousal visa application?
If I let them know if my mistake and tell them the whole time I've been in and out the country will this make any difference?

Please be kind. TIA

As you are now aware that HMRC must be informed of a change of circumstances (your absence) if you do not, you are committing benefit fraud. You are legally obliged to inform HMRC whether you want to or not.

As Amber says, you've committed benefit fraud. It's better for you now to be as honest with HMRC as you can be otherwise you're just digging a bigger hole. Once the matter is sorted (overpaid money you weren't entitled to paid back) it shouldn't have an impact on your visa application as the matter is resolved.
Apply while it's unresolved and it's a different story.

They will find out one day and when that day comes it will hit a lot harder than if you own up sooner.
Like you say; you've been working and paying tax. The working/paying tax part will definitely have you found out. It takes it's time (sometimes up to a year or two) but when the systems do reconcile and they figure it out not only will you have to pay the money back but you could end up with a fine imposed on top and potentially a conviction.
It's better you tell them now than UKHO figures it out when you submit the spouse visa application (as of course evidence of your relationship could be your travel to/from Mexico).

If money has been problematic, do you meet the £18k financial requirement when you've been working abroad?
Given you need to evidence this from employment (if you're not relying on savings) and submit bank accounts along with that employment it's highly possible it'll be clear to the CO you're committing benefit fraud, no?
You need evidence of earnings the equivalent to £18,600 for the 6 month period prior to submitting the application and has a confirmed offer of employment in the UK to start within 3 months of arrival (or be currently employed) meeting the minimum earnings level of £18,600 p.a.

If you're under the threshold and hope to make the shortfall from employment with fraudulent benefit payments that won't work either.

^ tad harsh and actually inaccurate rssfed. What amber said, and what is correct, is that it's only fraud if it's now not reported. The definition of benefit fraud according to DWP is "DELIBERATELY not reporting a change of circumstances". It doesn't fall under "obtaining benefits fraudulently" as the claim was intially made legitimately.

Either reporting it now or letting them click on, as child benefit is not a benefit that can be reduced or stopped when benefit fraud occurs, the penalty is wholly punitive (to be clear, your claim will be changed to reflect your ineligibity to receive it rather than the benefits being stopped, technically 2 different things). You will likely be interviewed to determine whether you deliberately mislead DWP. Obviously, this will look a lot better on you if you come clean as it can be explained as you just realising your error when you had reason to check. You will subsequently receive a fine (likely 50% of what you've claimed), but there will likely be a further punitive penalty (fine or custody) if you are deemed to have been dishonest and thus committing fraud.

Ultimately, linking it back to your visa application, it certainly has the potential to see your application refused if you don't come clean (they may also realise from any bank statements you produce), whereas this is less likely to be the case if your case is closed as the status is changed, you stop receiving the benefit and are officially seen to have made an "honest" mistake.