Exdp not using the correct car seat please advise

[Ponderfully]

My daughter was dropped back to me yesterday in a booster seat. She only weighs 19kgs. The law in my country is no boosters seats til they are 22kgs and it is advised to use high back booster seat until they are 36kg.
I'm blue in the face telling him and the exmil that she needs to be in her proper carseat. It's illegal but they don't seem to care. She was rearfacing until she was 4 and a half and they now think she's grand in a booster. The mind boggles.

What can I do? I've already pleaded with them. I just don't understand it. I've said they are not having her until I'm assured she'll be safe with them. They did not agree. They said they didn't trust my sources. It was a government website.

Can you get some informal legal advice? Like the half hour free that some offer?
That's not on and I think having some sort of official documentation might give him the kick up the backside that he sorely needs.

Where are you? Can you get some advice from the police?

Send them the link to the government website which makes it clear that it's the law?

I have sent him links. I live in Ireland. They know it's the law, they just don't care. Can I withhold access to her until they agree?

Could you give them your car seat each time they collect her and supervise them putting her in the car in it? In theory they would then return it when they bring her back in it. I realise that may not work but that's what we did when DSD told her she wasn't in a booster seat with her mums family, we ended up giving them a spare one.
You are in your rights to stop contact if you don't believe she's safe but if that's the only issue then I'd try everything else before stopping the contact.

Either don't allow them to take her in the car or contact police.