When my children were small, they rarely played alone while we were passage making.
Small children need help eating (balancing a bowl), drinking (there's nowhere to set a cup), playing (the toys keep falling over), finding things, and going to the bathroom (that's not too much of a problem because you're probably still in diapers).

They need to be entertained and comforted. If they get seasick they need to be monitored for dehydration.
I kept a supply of Pedialyte on board for this reason.
For seasickness I used Phenergan tablets.
The kids would doze for an hour, then wake up feeling well.

Sleeping can be a problem if there are only two adults.
You have to work out who will be on 'boat watch' and who will be on 'baby watch'.
It's difficult to do both at the same time.
Luckily, babies sleep sometimes.

It's good to get your little one out in the cockpit for fresh air.
Actually, it's good for the person who is taking care of the little one.
Put the baby in a life jacket and harness him to the boat, then give him a stick and a bit of string.
Kids can "fish" for hours.
They also like to drag "boats" behind the boat.
A boat can be anything-even a piece of aluminum foil.
When I got tired I would encourage games where I could lie down and play...just like anyone who lives in a house.

When there's a lot of motion, my kids tend to stay laying down.
I make sure there's a water bottle nearby each of them.
If you lay down with your baby, you don't want to keep getting up; try to have a water bottle handy, some toys, some food, and diapers.
Also baby wipes and a rag (to clean up).
I have several changes of pillow cases handy in case someone gets seasick (it's the first thing they hit), also towels; if you have to clean the settee it will be wet, but you can lay on top of a towel.

Don't let the things that sound hard discourage you. It's not as bad as it sounds.
Every child is different, so you will probably come up with many unique solutions that work for you.

Good luck.
I hope your trip works out.

One more piece of advice; don't wait till your baby get older because you heard it gets easier, it doesn't really--it just gets 'different' not necessarily easier.

Go while you can!