Your question is deceptively simple! But you'll need to do a lot of research. Ryanair's flights to Milan do not go into Milan itself, but to Bergamo (Orio di Sera airport) someway to the east. However you can connect to Milan or even go further east to Lake Garda, Verona, Padua and even Venice by train.

Perhaps I can be of more help if I respond to your question by some of my own .... and other members may be able to help too.

1. What sort of a place do you want to visit? Seaside, Lakeside, Countryside? You may need to look for somewhere that is relatively flat (ie not in the Italian Alps).

2. How far are you prepared to travel from the airport? I'm not really sure what you are looking for ... a villa with a pool in the middle of nowhere, or a seaside appartment with a flat prom?

I'm not sure that Ryanair's Milan airport is the best place for you to start your holiday because you will need to drive at least 3 hours to get to a family-friendly resort. Might you look to see if there is anything to FORLI - Bologna where you could easily access Ravenna, Rimini, Bellaria - beaches and flat access, or TREVISO or MARCO POLO airports - nominally Venice for Ryanair - and explore the beaches close to Venice such as Lido di Jesolo.

As it stands I can only think of your going north to Lake Garda's eastern shore, where there is a theme park called Gardaland, but I think that this part of Italy would not be the most enjoyable as regards what your children are hoping for from a holiday, and being in the lee of the alps, the weather is not as reliable as elsewhere.

You might find the 'tried and tested' resorts in Spain or the Balearics cheaper and more accessible for your handicapped son, and the cost of self-catering would also be lower. I'm not trying to suggest that you can't find the holiday you want in Italy, but I think that just because Ryanair have cheap flights there at the moment is only one element to planning the holiday that you would like to have, and that there are better locations as regards children's holidays and accessibility than northern Italy. And unfortunately northern Italy is NOT cheap! My OH and I often 'nip into Italy' for short breaks and sadly note that the cost of living is not as cheap as it used to be.