Talk to your accountant, OP. She/her will be able to instruct you on how to set up both so you get the employer deductions.

My employers give me a check at the end of the year for a 401k contribution. They pay for my healthcare insurance straight out. I chose and signed up for a plan at hire and they accept the monthly bill.

Do you use a payroll service? You can offer insurance as a stipend pre-tax. We just write our nanny checks for that purpose.

No idea how to do the 401k. I would up the PTO, obviously. Maybe consider paying for her phone?

Our PT nanny recently told us that she wanted to go FT and as it fit perfectly with our situation (baby on the way), we readily agreed. As a part-timer, she has had guaranteed pay and PTO, as well as cash bonuses at the holidays and on her birthday.

Now that she will be full-time, what benefits should we be considering?

1. Transportation is not an issue (everything is within walking distance and she lives around the corner from us).
2. Health insurance - how would we go about this?
3. Employer matching contributions to 401K/IRA - also no idea how to go about this.
4. What else???

BTW we would space these out, e.g., offer insurance now, retirement contributions a year later, etc.