Anonymous wrote:"As we mentioned, it is too advanced for him. I did some online research, and it seems this gift is best suited for ages 8 and up. We will save it for later. Thank you for the thought."
If she asks again, respond VERBATIM.
This -- but OP, your husband has this talk with his mom. You do not.
Adult children handle their own parents when those parents start carping about nonsense.
If your husband is not willing to tell his mom that son will enjoy the toy when son's a bit older, then husband is an issue himself. I hope he will use the script above and tell MIL nicely and firmly what PP recommends. Repeat as needed.