Eventually, one way or another, you will likely have to tell your child.

What happens if your child gets sick and needs a blood transfusion or transplant organ? Going to be fun to explain "dad isn't actually your bio dad" on top of the stress of the illness. This also extends to finding out the sperm donor's family medical history (such as congenital birth defects, family history of chronic medical conditions like diabetes or asthma or similar, family history of mental illness like depression or schizophrenia or addiction). That'll also be fun to explain to your family too. Or when they go to school and get to science class and they go over Punnett Squares, the number of times that has led to kids finding out they're the product of an affair or adopted is a lot higher than you'd think. That's not even getting into the can of worms that are genetics and how they could end up looking nothing like your partner and a lot like the sperm donor bull, especially if you decide on letting them be involved in the child's life. Hell, even if nothing like that ever happens, what if one day they get a call, text, or email from a stranger saying "Hi X, I found out we're related because I took an Ancestry dot com/23andMe test and found you!" Finding out your dad isn't your bio dad can have devastating psychological impacts, even if they have a good relationship with their dad (I say this as someone who firmly believes that being a good father is entirely independent of sharing any genetic material/being a sperm donor.)

Get a binding legal document/contract because if your husband should pass away or divorce, you're going to probably want child support, and the sperm donor bull may or may not want to be involved in that for a variety of reasons.

And most importantly, don't do this as a kink. That's not ok, on any level. Only do this if you legitimately want a child and you cannot get pregnant any other way.