Advice/thoughts

Hi! I need some ideas/advice on what to do with the extra money I have in my bank account per month. Here are some details about my situation:

• I’m 30 and I live in NL (no 30% tax ruling, expired)
• I make €240k a year base salary, my partner makes €100k (gross salary, not including bonus, RSUs).
• My mortgage is €1.3k a month at a very low interest rate (so not really interested in trying to pay it off super fast)
• My monthly expenses are about €6k a month including mortgage (I have twins, daycare is expensive in NL)
• We currently transfer 1k€ a month in a “high” (as high as it gets in NL for me at 2%) savings account for the kids
• We transfer 3k in Degiro for a mix of stocks and ETFs
• We have 25k of emergency funds

We have a healthy leftover of cash per month, any advice on where we should be putting it?! Would like to try and retire around 50-55...