We often find the restaurants that are slightly out of towns are more likely to have outdoor play areas for the little ones. I know the pollensa area better so if you are planning on visiting there and need any info just ask.
Have a great time, we are visiting in July and will do the Palma - Soller rail journey.
Edit; couldn't remember the name of the one near the beach in Puerto de Soller but a quick search and it is called Es Raco. More a beach restaurant but very good food and they were great making a special meal for my daughter, just googled it and it gets rave reviews on Trip Advisor as well.
Last Year, we had a nice Finca near Cala Murada for the holidays. For dinner, we mostly went to Felanitx. There is a nice restaurant called "Estragon". They were very friendly to all the children there. An there were many of them :-)