I have 3 children and go WAY over the top and have never come close run out of ideas/options (although running out of money/space can be a big issue).
There are litrally BILLIONS of toys for kids, its one of the most saturated markets.
The issue is actually not being able to buy ALL the different thing (there has to be a line in the sand somewhere).
If you walked in Smyths or the Entertainer right now are you saying your kids own anywhere close to every age appropriate thing that could apply to their imagination or interests?
Its impossible, especially with new things coming out daily (between each of my children so much changed and the smallest age gap is only 2 years).
You just have to walk in a shop, watch kids tv or open google to be assaulted by 100s of ideas of gifts for kids.
I would also counter argue older kids are much harder/worse, my teen is by FAR harder to buy for, apart from his Xbox and Minecraft game he hasnt wanted or played with anything else for over 5 years.
He might aswell be a grumpy old man saying 'bah humbug'.
Toddlers however have huge imaginations, require specific age appropriate learning tools (hand eye co-ordination etc...) and actually WANT to play and need constant entertaining hense why the big market exists.
Some toddler stuff can also be picked up SUPER cheap, they dont care about it being secondhand and are usually happy/excited with virtually anything (its the cutest age).
Up until 8 is by far the easiest ages to buy for.