I play guitar and drums. And I have both ...

My son really enjoys messing around w/ my instruments so for christmas last year when he was 6 I got him a jr size drumset.

Firstly part of the reason I did so is no matter what I did the fullsize was just too large/unwieldy for him to use. Even when I lowered my throne (seat) then he couldn't reach the upper half of the set. He literally had to stand at my drumset to try to use it at all.

The jr size set on the other hand is perfect size and works very well for him.

I considered more expensive sets but after a bit of reading I got him this GP Percussion set off of Amazon

https://www.amazon.com/gp/product/B000OIQZPW/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

And it was a great decision.

Pros:

• these are 'real' drums with lugs and can be tuned
• very nice quality
• perfect size
• very nice price

Cons

• cymbals are cheap starter cymbals (as they are with every set so this is not particular to this set)
• the bass drum pedal is a "belt" drive and feels too lose to me (I use chain drive pedals)

But the cymbals and the pedal can be upgraded if your kid ever takes the playing seriously and if not they are serviceable.

Your kid is 4 - this will be a toy to them. As a musician and a father I support my kids interest in music but until your child shows actual sustained interest and commitment my advice is do not overspend just because as a musician you might understand ' you get what you pay for' in an instrument.

Your child will most likely play with it for a while then forget it exists and sub $200 is a lot easier to throw away than $600-1200 on a toy.