I don't regret those purchases. They have been fit for purpose, but over time we came to want quality kids bikes too. Kid's bikes that didn't weigh a tonne, bikes with decent mudguards and components, bikes that would last and be handed down through the family and even still have some re-sale value at the end of it.
Now we are looking at 24" wheel bikes for Isabel; the lightest (an Islabike Beinn 24) is 10.3 kg, the next lightest comparable models (eg., Dawes Tracker) are mostly 12.2kg+; that extra weight is almost 10% of her body weight! It's like asking me, a 60 kg adult, to consider two otherwise similar bikes, one that weighs 25 kg and one that weighs 30 kg. Would anybody seriously think twice about that?
It's bad enough that even the best quality kids' bikes need to be so heavy relative to the weight of the child, but don't make this weight disproportion even worse than it has to be.
I totally understand people who don't want to pay out even when they know about the quality difference. But if you can afford it or make it economical in the long run (lots of siblings to pass the bike down to!), it's a nice thing to treat your children to -- and essential if you want them to enjoy the habit of regularly riding long distances with you.