Go for 4 or stick with 3

I have a 3,5 and 6 year old. GGB - I’m seeing alot of the 3rd kid issues. My two girls are super close in age and basically besties.

My heart is torn - is it a good enough reason to have another baby to have an even number of kids???

So they can pair off together. We are home alot and they love playing but I do see my youngest son being left out. My girls try to include him but he’s quite destructive being age 3 and just not on the same page with playing.

Is 3 really harder than 4 - I need to make up my mind as time is ticking and I don’t want a huge age gap if we do go for it a 4th.

Any advice please?!!