My almost 5 year old and 3.5 year old are under 20kg so fits most toddler attachments still
I am not sure about prams, best to go into a baby shop and have a look, but you CAN get a cool bike that attaches to the side!! So the kiddie can sit... ill see if I can find a link!

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Tricycle as a Stroller Attachment- HotSpotMama Find

I looked at them in the store They attach to the side of the pram, so they aren't in your way like a buggy board, and look like great fun for the kids!! The one at my store was $108, so teamed with a affordable stroller (I got a great 3 wheeler for $179) it can be a lot cheaper!

Roger Armstrong Elfin 2 Stroller Reviews Australia www.rogerarmstrong.com.au
This is the one I have. I LOVE it. 1 handed fold down, nice sized basket, pocket on the back for mummy things, came with kiddy tray and boot cover, nice and compact/small/light for a 3 wheeler!