Ikea furniture life depends heavily on the owner. They've done well at my house with kids ages 4, 7, and 18 but haven't survived long at friends' houses.

We've had a hand-me-down Billy bookcase for over 10 yrs and bought a second to match it 4 yrs ago. The original held dozens of engineering textbooks for years (even though ours was fine, I do not recommend it). My now 18 yr old used them for 3 years, and for the last year my 7 yr old has had them in his room.

We also have 2 Kallax 4x4 shelves bought 4 yrs ago when our youngest was born. They were both anchored to the wall and housed in the playroom with canvas boxes holding toys. Now, we've moved and the kids are older with less in the playroom only using one Kallax, so we're using the other to hold all the engineering texts in the office. (Much sturdier solution, works great)

Also be aware that the top Billy is standard depth and storage behind the doors will be very shallow, at only 10.5" while the Kallax has cubbies that are 15.25" deep and provide more toy and book storage. If I were you, I'd get the Kallax 4x4 or 2x4 over the Billy with doors. I can see the doors being a week spot and kids wearing them down.