First, I would tell the small company, you've been 'approached' and you are considering leaving for the challenge
Do NOT do this. That is single handedly the worst advice you can give someone.

You never mention that you might leave. Never, ever ever ever. The second you do, they will start looking for a replacement and clear you of your responsibilities. Even if you end up staying, you're already slowly out the door.

We work in IT. Nowadays, that is the fourth leg on every company's business table. Most every employer will tell you - because of the importance of what we do, loyalty and dependability is a major factor in this line of work. Threatening to leave if we don't get our way is not a card we're allowed to carry. While it's not extortion, it's deffinitely a close cousin.

Approach the company you work for and ask for a challenge (or better yet, bring one to them). That much is fine. If they will work with you and allow you to pursue this, then great. If not, then look at the other position.

Also, earn your worth. Job jumping is fine when it's just that - a job. Based on the salary, it sounds more like you're on the career path. And unless you have clear cut reasons for changing companies alot, you're going to immediately raise two red flags for every future employer - no loyalty, no dependability. Which means, you will fight an uphill battle in every new position to take on any new responsibilities.