MIL let DD aged 5 get sunburned but DH thinks we should just be grateful she had her and gave her a nice time.

You are being unreasonable. Mine have been out all day in shade. In and out of the pool with sun cream and still got burnt.
put her in a rashie next time. Décathlon have them.

Yeah she should but also. I don’t think my parents knew sun cream existed in the 80s/90s and I’d not be lying if I said I was probably 18 before I actually put any on.

This is much like when posters go well your mil can’t be that bad she raised your husband… like that excuses fuck ups than continue to get made.

Your MIL should really know better.. after all she has been a parent herself! You reminded her about reapplying when you dropped your girl off, she should have really been on it. All those saying she might not know suncream washes off..?! 🙄 Yes, thank her for having her, ask if she did put more on, because look….
*or she might not feel the need to, next time.

Tbf it’s the first proper hot spell of the year and sun cream even if applied regularly isn’t necessarily enough. My dc are half Cypriot with olive skin and still need to come out the sun even with cream on at this time of year. I’d have sent a rash vest of water play outdoors was on the agenda

How about having a grown up conversation with your husband and MIL.

The world has been warned about the damage re sun rays and skin cancer for years.

Has they both been living in a cave?

This had me torn, as a GM I would feel so upset if I was sent a picture of my Gds sunburn and very guilty. I am sure it wasnt done maliciously and I know its no excuse but you MIL is from a different age we used to have salt baths to "take the sting out" and maybe she just forgot when she had lots of grandchildren to care for, mention it but dont send a photo unless shes such a dreadful GM you dont care about your relationship going forward. Maybe get your husband to say it. I would be very sorry but it would depend on how I was told no one likes to feel lectured or humiliated.

You learn very quickly that these things happen. I have 4 kids and it’s happened to me even with applying suncream. Water especially makes it worse. I would say chalk it up to experience. I found the easiest thing was to put them in a big baggy tshirt when in the paddling pool with a pool hat on.

I’d be fuming personally, I have a very fair haired child and have to reapply frequently.
You’ve mentioned the plan had changed which is why she didn’t have her usual costume, it might be worth in future always packing it/leaving a spare.
I would say something on the basis that if it were my own mother I would absolutely say something about it, I don’t see why a MIL shouldn’t be told that she’s allowed her get burnt on her watch.
Sorry but to me, it would be a form of neglect. When I’m looking after my nieces/nephews I’m always more cautious with them then my own children.
I don’t think I know any adult within my direct family that would let a little one sit in a paddling pool with just her knickers on and not think to put it in the shade, pop a t-shirt on her or reapply sun lotion very frequently.
Your DH bar must be very low if he thinks you should just be grateful that she ‘looked after her’ which tbh she didn’t do an adequate job of!

Because she was meant to be on a forest walk not a pool day.

Upsetting but why didn't she have a rash vest on?

This is the way to go

I’d speak to her face to face and show her the photos. Be clear about what sun protection is required. If she won’t do that, then no more babysitting.

I was also going to say that the sunscreen may well have been out of date. In addition did you clarify what factor she was using. I would not use less than factor 50. Also you need to be making sure that young skin stays in the shade.

If child is burnt badly enough to be in pain then that is serious burn. Granny needs to be told in a factual way. You can include yourself in the “let’s learn from this conversation”. Tell Granny that the bloody sun is dangerous. “We” can’t let her get burnt again so going forward this is what we will do…. I hope she feels better soon.

Send the photo. It will serve as a reminder for next time

This. It’s not a base tan it’s sun damage. Skin cancer is no laughing matter. Irresponsible at best from MIL.

Don’t send a pic, tell her that your DD is in pain and sore. We don’t know how to handle the sun in the Uk (assuming you’re here), people in routinely hot countries aren’t out damaging their skin in the hottest part of the day. As I say, irresponsible at best.

This l agree

This

Also saying something next time bundles it up with the normal process of a few words about what the child requires before leaving a child in someone's care.

Sending a photo now is a "thanks for nothing" complaint. I understand you are cross but I think you can achieve the practical outcome you need without that.

This is what I think.

Providing or requesting photographic evidence is normally to corner someone, so it's quite an aggressive way to start the conversation.

Just provide a hat and rash vest in future and a bottle of sunscreen and say she needs more than last time as she had sunburn. If she doesn't believe you you can show it then, but why go in guns blazing till you know if she is apologetic and receptive?

I've no idea why you think I believe it's the child's fault they got sun burned. If you've read my posts, you'll see I suggested a multi-pronged approach to managing days out in the future - checking whether the MIL/babysitter did actually put suncream on/have the pool in the shade; pack for all eventualities and teach the child about expectations. Some posters picked up on the latter and commented on that only, which I then responded to.

If it is a normal part of the process that suncream is applied before swimming/during a break etc., then the child grows up expecting this and asks if it's time to put suncream on, or gets it out of the bag and puts it on their arms and asks a grown up for help putting it on their back etc. If you expect absolutely nothing from children, that's what you get.

My mother would be devastated to receive such a photo. I have friends who have misjudged and seen their own children get sunburn in front of them.

It was an accident. Do not send that photo.

Be much much clearer the next time. Tell her multiple times and tell her the timings. Write them down on a piece of paper and read them out. Tell her you'll be sending reminders and do it. Explain DD burns easily and then in person say sunburn developed after you picked her up the last time.

Just knickers with no cream on on a hot day without suncream is negligence. She needs to know about the sunburn, and I wouldn’t leave her with my kids unsupervised until they’re old enough to remember own suncream (16?)

Agree with this

Well you can but dew people wpuld expose that micj skin in those conditions.