Kiddy impact cushion - age or weight?

[Chocchip88]

We have a Kiddy Guardian Pro. It says the impact cushion is to be used up to 18kg or about 4 years old. My almost 2 year old is almost 18kg (very tall!), I assume I am still meant to use the cushion once he's over 18kg as he still be way off 4. Can anyone confirm?

It is always the weight that is the most important when it comes to car seats :(

This car seat http://www.incarsafetycentre.co.uk/catalog/product_info.php/products_id/46 two way elite has a harness until 25kg

link so it will work two way elite

DD1 is a bruiser and not 4 till late november but has been in a kiddy cruiser(?) (one without the impact shield) for a nearly a year

Oh, not sure I'd be comfortable with him not using the impact cushion at this age. Will hope he stops growing for a bit