These nuts with spiny shells look a lot like what I called Horse Chestnuts as a child. Told they were toxic.
Yes (toxic) although they can be boiled to leach out the toxins. Somehow squirrels can eat them, although I am suspicious that if they eat too many...
More complete info.:
https://www.quora.com/Are-buckeyes-poisonous-for-humans-What-animals-usually-eat-them