What I learnt from two days of car seat research about convertible boosters - long and boring :-)

At beginning of the week I had a few simple questions about car seats - I thought it should be an easy task to work out what would work best for a 24kg almost 5 year old DD and an 18.5kg almost 3 year old DS - I was completely wrong.
I had a couple of simple questions about convertible boosters (type B/E) so ones that are a harnessed car seat but can then be changed to a booster using the lap-sash belt for restraint (advertised as 6m to 8y e.g. EzyLove Combo, SnS Meridian Easy Adjust, Infasecure Caprice)

1. Does the change to booster mark on height marked convertible boosters, mean once shoulders reach that point then you are safer in booster mode than staying in the harness?

2. What is the best solution for a tall child who will reach the change to booster marker before they are four years old (it is a legal requirement to stay in a harness until they are 4).

You would think that a quick google should such resolve such things, with this type of information being available on ‘official’ websites. E.g. Car seat manufacturers, Australian Child Restraint Industry (ACRI), VIC Roads etc. etc. but apparently not.
In 2010 the car seat standards changed and they became based on height and not weight. I think the key problem has been that this change has not been managed very well – with lots of sites not being clear, using old information etc. – and really just not thinking about the sort of questions people who had been used to the weight based system would ask.
These are the Q&A questions I have made up to answer my own questions (I have suggested that ACRI look at including similar in their FAQ, and they are looking into it)

Q. In a convertible car seat should I change my child to booster mode when they hit the change to booster mark?
A. The seats are designed and tested to be moved into booster mode at the change to booster mark. Different seats have different height markers for change to booster mode as the current standard only mandates the minimum height these markers can be placed at. If your child is under 4 or you prefer a harnessed seat you might want to investigate other seats shoulder height limits before changing to booster mode. (See below – height limits)

Q. My son is in a convertible booster beneath the height markers but weighs 28kg - is this restraint still suitable for him?
A. Yes providing your son has not reached the change to booster markers, his restraint is still suitable.

Q. My daughter is 6 years old and 35kg is 120cm tall she is beneath the height markers - is her booster seat still suitable?
A. Yes if your daughter is beneath the height markers at the top of the booster, it is still appropriate to use a booster seat.

Height Limits
(I am specifically talking about convertible boosters)
The markers on seats are all different - and there appears to be no single place where you can find out what the markers are. (You can go and ask on various FB groups – but personally I don’t think this is satisfactory and you should be able to see them on the internet). So different seats have different change to booster markers meaning some you can keep your child in a harnessed booster seat far longer than others. (I myself have measured some as low as 38cm others as high as 45cm). If you have tall torso children this can be particularly important as you can end up reaching the change to booster marker before they are 4 and legally allowed in just a booster. Also you might just prefer a seat with an inbuilt harness for longer. Some websites do list the height markers of their individual seats, but none appear to do so in a table and some are not accurate. E.g. They have updated seats to give higher markers (they do further testing on the seat and can then raise the change to booster markers with new covers) but website does not reflect this. The whole situation is very confusing for the consumer and I personally don’t think having to take your kids to various shops to try them out in the shop is satisfactory, you should at least be able to narrow down to the appropriate height range on-line before trying anything out.

Please correct anything you think I am wrong on.

Thank you! It's all so confusing!!
Do you know when I have to change DD1 to a booster? She is still using a MaxiRider without height markers, with the inbuilt harness. She is 5 years old but only little, i.e. I think only between 15 and 16 kilos, lol. Found the info I got with it but it doesn't even say, just says you can change them at 4. I want her to stay with the 5 point harness as long as she can.

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Thank you! It's all so confusing!!
Do you know when I have to change DD1 to a booster? She is still using a MaxiRider without height markers, with the inbuilt harness. She is 5 years old but only little, i.e. I think only between 15 and 16 kilos, lol. Found the info I got with it but it doesn't even say, just says you can change them at 4. I want her to stay with the 5 point harness as long as she can.

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This is one of the issues I think with the change over, it isn't that clear. If the MaxiRider doesn't have height markers it will have a weight limit (probably 18kg) - so if it is 18kg then providing her shoulders aren't more than 2.5cm above the top harness slot. I think the main thing have learnt is that you should always follow manufacturers guidelines, but don't worry about age - age is only really in there due to the law mainly - rather than safety, also if the seat you have doesn't allow you to do what you want e.g. keep harness there is likely to be another seat that does, but finding out what that one is, is not as easy as it should be.

The FB group that has lots of information is called "‎Child restraints. Is your child restrained correctly?" - does appear to have lots of info on what height markers are in the different seats, and also if you need to fit 3 across what fits in different cars.

It does have some people who work for car seat manufacturers in it, so bear that in mind - it is difficult to tell how impartial the info is.

Also car seats are about risk minimization, the site is very pro extended rear facing, which is fine, but personally I think advice about giving 6 months olds food, or propped up bottles, or DVD players just so they will be happy to rear face, ignores the risks that these things have (particularly the food) and while it is up to individuals to assess what is best, I am not entirely comfortable with the stating of the risks of forward facing, without mentioning risks of food (at 6 months it is usually recommended that you can see and easily access a baby while it is eating/sucking on food) etc. etc.

Thank you for your findings in research. I was following the other thread too as I was looking for narrow seats, for similar reasons to you, small car and not being able to fit anyone else in, and dd has outgrown her current one at 6 years. I was really interested in the infa ones since they are very narrow, but the height wasn't enough. I ended up getting another safe and sound hi liner as that was the only one that gave the height I needed.. And reluctantly gave up on my idea of possibly fitting a 3rd person in the back.

Thanks wysiwyg! That's good because she's nowhere near outgrowing it height-wise either.